RP 334X

PREFACEThe following Recommended Practice is subject to the Disclaimer at the front of TMC’s Recommended Maintenance Practices Manual. Users are urged to read the Disclaimer before considering adoption of any portion of this Recommended Practice.

PURPOSE AND SCOPEThis Recommended Practice (RP) provides equipment users with guidelines for establishing engine oil drain intervals for heavy-duty diesel engines. This RP neither endorses nor discourages the practice of extending oil drain intervals. This RP covers all heavy-duty diesel engines (8.0 L and larger) operating on ultra-low sulfur diesel (15ppm max.).

SECTION I INTRODUCTION

Engine maintenance frequency and oil drain intervals are established to optimize component life-cycle cost, reduce downtime and emergency road failures, improve emissions, and ensure safe vehicle operation.

Manufacturers of heavy-duty diesel engines provide recommendations for oil and filtration performance levels and recommended drain intervals. Manufacturers’ recommended drain intervals are prescribed using thousands or hours in a test cell and millions of miles of field testing across a multitude of operating duty cycles to provide engine reliability, durability, and reduce warranty claims. However, since equipment users are often most interested in optimizing engine performance, operation and return on investment, there’s an interest in determining safe and economical condition based optimized oil and oil filter service intervals without sacrificing engine durability or dependability.

NOTE: The owner/maintainer should consult their truck, engine, lubricant, oil analysis laboratory and oil filter suppliers when attempting to optimize oil drain intervals. Each supplier will bring valuable resources and knowledge about their products and the impacts that the optimized service intervals may have. Strong collaboration will be critical to the success of the project to ensure that the service interval does not compromise the durability and reliability of the equipment.

This RP offers guidelines for establishing oil and oil filter service intervals and suggests several procedures and recommendations which may be incorporated into the maintenance program. This document has been developed with the assistance of engine, lubricant, additive, filtration, oil analysis laboratory and aftermarket manufacturers, and fleet maintenance personnel.

SECTION II DETERMINING OPTIMIZED OIL AND OIL FILTER SERVICE INTERVALS

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GUIDELINES FOR ESTABLISHING PROPER ENGINE OIL AND OIL FILTER SERVICE INTERVALS FOR HEAVY-DUTY DIESELS

VMRS XXX-XXX-XXX

Determine how the optimized service intervals (OSI) will impact the existing preventative maintenance (PM) intervals and overall program. It must be kept in mind that other service intervals have been established by the OEM's in conjunction with the oil and oil filter service intervals (i.e. chassis re-greasing, fuel and air filters, drive-line service intervals, brake system air dryers, etc.) The fleet must coordinate these requirements with the targeted oil drain interval in accordance with OEM service recommendations. In some cases this may require the use of other OSI products. The oil and oil filter intervals must be incorporated into the broader PM program in order to aid in reducing the overall maintenance cost and to increase the efficiency of the valuable maintenance resources.

Various engine makes, models, EPA vintage, application types, and oil and oil filter types will support different service intervals. The duty cycle(s) that the fleet is operating under need to be determined before attempting to optimize oil/oil filter service change intervals, see Section VIII Duty Cycle Characteristics. The duty cycle will aid in understanding the amount of stress the vehicles are operating under and hence the potential to optimize service intervals. The information used to determine the duty cycle will also help in conducting a feasibility analysis (Total Cost of Ownership model, TCO) or benefits as a result of the targeted optimized service interval(s). Key variables needed to determine the duty cycle include; fleet’s/division’s average mpg, annual miles, percent idle/PTO time, and gross vehicle haul weight. Average operating speed will also help to understand the severity of the fleet’s duty cycle.

Engine OEMs provide their service intervals based upon duty cycle and operating condition in terms of mileage or hours. Duty cycles that include high idling and or PTO time may be time dependent. Lower average speed operations may also be time dependent. Some fleets may operate under multiple duty cycles and each variant needs to be incorporated in the final service interval determination.

A total cost of ownership model must be developed to understand the overall “value” of the optimized service intervals in order to assess the return on investment (ROI) of the project. This will also aid in assessing the risks and rewards associated with operating under optimized service intervals. The cost of the used oil analysis program needs to be included in the TCO analysis. The fleet will need to secure internal resources to manage and steward the OSI program from testing to implementation. The following considerations may be included in assessing the need for internal resources; does the maintenance program support multiple/customized service intervals, training, man-hours to pull used oil samples, equipment to secure the used oil sample (i.e. engine oil sampling valves), interpretation of the used oil analysis results, etc. Strong collaboration with Operations, Drivers, Mechanics, Dispatch and Management are vital to the success of the program.

The OSI process will evaluate the condition of the oil and oil filter throughout the service interval and their impact to the engine’s reliability and durability. It will also evaluate the amount of stress the engine’s operating conditions will have on the oil and oil filter, i.e. soot loading, acid generation, heat stress, etc. which may impact the service interval.

Oil and oil filter(s) selected for the OSI investigation must be approved for the engine(s) and severity of duty by the engine, lubricant and filter manufacturer. Whatever oil and filter(s) are chosen for the trial ideally should not vary as it is not certain that others would yield quite the same optimal service interval measured. The method in which oil changes are performed must be conducted in a repeatable manner. The oil change should be conducted according to manufacturer's instructions, i.e. changing while the oil is warm/hot (may need to run a cold engine to warm it up). Performing a hot oil change allows the oil to flow more readily, results in a thorough oil drain and reduces the amount of aged oil carry over from the prior fill.

Maximizing life of the oil requires that the engine be sufficiently drained of its oil prior to filling. Residual degraded oil has many negative effects on the fresh oil and proper steps must be taken to minimize used oil carry over. These steps include; 1) making sure to replace the oil filter after each oil change, 2) allowing sufficient time for drainage, particularly from the engine upper end, 3) drainage from all ports, as some have multiple low spots with additional drain plugs. Consistency is key for achieving a successful OSI program. The maintenance practices applied during the OSI test must be applied after the OSI program.

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Engine manufacturers make upgrades to engine designs every year and maintenance practices can be modified at the same time. Some of the original maintenance practices followed during the OSI test may or may not be applicable with every engine make or model. Consult with your OEM and engine manufacturer to incorporate any applicable maintenance practices.If fleet conditions significantly change, it is recommended to conduct a follow up OSI test to understand how the new fleet conditions impact oil performance and therefore the OSI. For example, the addition of APU’s (Auxiliary Power Units) would likely reduce idle time. Reducing idle time is beneficial for longer oil life.

Another example of changing fleet conditions is a change in engine oil supplier. Each engine oil supplier formulates their oil differently and each formulation can behave differently in the same engine. It is important to conduct a new OSI program when changing engine oil suppliers.

Preparatory Activities The following activities/considerations are needed before a fleet embarks on an OSI program:

• Review current maintenance program to ensure PM intervals are being performed properly and on time and according to the OEM recommendations. A missed PM service during an OSI program may create an added risk to the equipment. If a historical review of the fleet’s service interval accuracy against target reveals delays, the targeted OSI should incorporate a margin of safety to prevent a loss of protection resulting from the added stress to the oil and/or oil filter.

• Chronic mechanical problems in the fleet are not conducive to an OSI program.• The oil, oil filter and oil analysis suppliers and engine OEM must have the expertise, products

equipment to support the goals of the OSI program. • Review historical used oil analysis (UOA) results (approx. one year’s worth of history), where

available, to understand the capability of the fleet to operate under the targeted OSI. It is critical to identify and understand the factors that may impact the targeted OSI. The history will also be used to develop performance baseline for the oil and engine(s). Consult with engine OEM to review the historical UOA results to determine the OSI capability.

o Admit only stable data: instability of data may be apparent due to changes which include a new or freshly rebuilt engine or a change of lubricant type. One common peculiarity that appears under such circumstances is excessive levels of Copper.

o Passivation is seen in engines having copper brazed oil coolers until an equilibrium state of passivation has been reached.

o In these cases, it would be best to delay data gathering for OSI determination until the copper based oil coolers have been passivated, typically within three oil drain intervals.

• Develop the test protocol to include the targeted OSI, duration of the test, roles and responsibilities of the fleet and suppliers (engine, oil, oil filters, etc.) and fleet locations to be involved in the study.

• While always challenging, establishing a baseline oil consumption rate is important to the results of the oil drain study. Ideally, oil consumption should be monitored and recorded throughout OSI testing period(s). An agreed upon tracking method should be incorporated in the testing protocol. Consumption is often non-linear and may accelerate throughout the interval. Increased oil consumption will 'sweeten' the sump with fresh oil and additives and may allow the drain to be extended. The oil consumption history will be used in combination with the used oil analysis results to determine the OSI.

• Best practice is to use engine oil sampling valves in order to ensure a representative and consistent oil sample. Check with your engine manufacturer before installing an oil sampling valve to ensure the valves installation does not negatively affect engine performance or durability.

Vehicle SelectionAn optimized service interval (OSI) study is used in evaluating the performance of a system, the vehicles and its components (i.e. engine, oil, oil filter, etc.). Historically, a good general rule of thumb used by the industry, has been to select 10% of the vehicles in the fleet to assess OSI.

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For large fleets this may be very difficult to steward. Experience has shown that selecting fewer number of test vehicles allows for generating higher “quality” data. Selecting five (5) to ten (10) test vehicles per engine make, model, and EPA vintage of like duty cycles has proven to be more advantageous. For example, if the fleet has a distribution of trucks with high MPG and low MPG or alternatively, high idle % and low idle %, it is important to select trucks on each side of the distribution. Only selecting trucks that are low idle %, and establishing the OSI based on this set, will not adequately protect the high idle trucks in the fleet.

The units selected should be representative of the majority of the fleet with respect to:• duty cycle • application • operating environment• horsepower • EPA vintage• etc.

The test vehicles should have the lowest number of operating miles/hours for the specific group of test trucks (new trucks must be through the “break-in” period). Duty cycles to be validated using the engine control module/unit (ECM/ECU). If the fleet has units operating under a variety of conditions/duty cycles, the most severe should be selected. Otherwise the OSI need to be customized by duty cycles and operating conditions.

Validation TestingAn OSI program is specific to each fleet but the following guidelines should be incorporated into all OSI testing programs.

Use interim used oil sampling (frequent sampling within each oil change). When evaluating the UOA results, the focus shouldn’t be on isolated data points, but the dataset

as a whole. The targeted OSI should include a margin of safety to ensure flexibility in meeting the targeted

OSI. A historical review of the fleet’s service interval accuracy against target would provide a basis for setting the margin of safety. It will help to prevent a loss of protection resulting from the added stress to the oil and/or oil filter.

The historical UOA results can be used to set an initial targeted OSI. When an UOA history is not available set the initial targeted service interval to the OEM’s recommended interval and assess the results for the potential to support OSI and to identify limiting factors.

In determining an OSI, the fleet can consider targeted drain intervals in increments of 10% to 20% based upon the performance at the previous interval. Review the oil analysis histories; with the advice of your engine OE, oil and filter suppliers, and oil analysis provider to identify the OSI (distance or time) where the stress to the oil has first become evident.  For each OSI this represents your best estimate of how far (distance or time) the oil could have run out to safely.

After validating the final OSI (distance or time where the stress to the oil first become evident) statistics can then be used to help identify the margin of safety and the “practicing” OSI.

1. Evaluate the used oil analysis history of several final OSI, as described above. 2. Calculate basic statistics, mean and standard deviation for the subset.3. The ODI will be the mean value less two standard deviations to take into consideration variation. 

Thus if the mean was found to be at 52k miles, and the standard deviation was calculated as 4k miles, then the ODI for that set of vehicles would be 52k-4k-4k or 44k miles.

4. With the ODI established keep a close watch on drain samples for the vehicles until confident that oil is not becoming excessively stressed. See Section X for establishing alert limits.

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NOTE: Statistics should be used on a larger sample size to increase the confidence level of the data. Smaller OSI projects will generate less data during the testing phase so in order to increase the confidence level of the dataset it seems practical to either run more testing intervals or add more test trucks, or to continue to include on-going data to the sample population or a combination of all of these.

Regardless of which method is used to determine the OSI, validation testing should include the completion of two (2) to three (3) service drain intervals at the final OSI to ensure reproducibility and repeatability.

Securing interim oil samples will aid in understanding the condition of the oil throughout the service interval and its impact on engine durability. Therefore, interim sampling will help identify where the stress to the oil and to the engine has first become evident. The interim sampling intervals need to be evenly spaced and should yield 4 to 6 (includes the end of drain sample) oil samples within the targeted OSI. For example if the targeted OSI is 40,000 miles the targeted sampling intervals should be 8,000 miles. Interim samples will describe the “rate of change” of the critical UOA parameters being assessed and aid in determining when the process is not under control, see Graph 1. Trend lines can be plotted for critical parameters (total base number, iron, chromium, lead, copper, soot/solids, silicon, etc.).

These trend lines to remain within control; trend should not display significant shifts in the rate-of-change.

The used oil analysis program, at a minimum, should include the following test slate; • Viscosity, oxidation and/or TAN, TBN• Foreign Contamination; soot, water, and coolant and dirt/dust• Metal Analysis: wear metals and oil additives

Filter performance is as critical to an OSI program as is the oil’s performance, see Section VI Oil Filtration. Selecting an OSI capable filter with the required durability and capacity is essential. Used filters will need to be tested by the filter supplier to ensure suitable performance at the targeted OSI. Engine inspections on the OSI test units should be strongly considered to validate the UOA results. It is important to examine oil-wetted parts to ensure un-expected wear or corrosion is not observed. Some engine components may be more susceptible to corrosive attack by degraded engine oil than others, and it is possible for these components to fail even though the UOA does not show any markers in the analysis.

SECTION III OSI INTERVAL COST-BENEFIT CALCULATION

While not all engine OEMs have a formal program to extend service intervals beyond their published recommendations, they may assist fleets in an advisory capacity to minimize equipment risks. Fleets are strongly encouraged to review any drain extension program with their engine OEMs/Dealers before initiating the program.

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Iron,

ppm

Miles on Oil XXX

XXX

Graph 1

The following formulae may be used to project the relative cost of oil, filters, labor, and used oil disposal plus oil analysis expense for a current service interval and a proposed optimized service interval.

Oil Drain Interval Cost Benefit Calculation

A Mileage Drain IntervalB Annual Miles per UnitC Oil Changes per Unit per Year (B/A)D Crankcase Capacity (gallons)E Gallons of New Oil per Unit per Year (C x D)F Per Gallon Cost of OilG Annualized Oil Cost per Unit per Year (E x F)H Oil Filter CostI Filter Change IntervalJ Oil Filters per Unit per Year (B/I)K Annualized Filter Cost (H x J)L Hourly Labor RateM Time Required for Oil ServiceN Labor Cost per Oil Change (L x M)O Annualized Oil Labor Cost (C x N)P Time Required for Filter ChangeQ Labor Cost per Filter Change (L x P)R Annualized Filter Labor Cost (J x Q)S Used Oil per Unit per Year (=E)T Per Gallon Oil Disposal CostU Annualized Used Oil Disposal Cost (S x T)V Oil Analysis Cost per TestW Oil Analysis per Unit per YearX Annualized Oil Analysis Cost (V x W)Y TOTAL Annualized Cost per Unit (G+K+O+R+U+X)Z Total Number of Units in FLEETAA TOTAL Annualized FLEET Cost (Y x Z)

Oil Drain Interval Cost Benefit Calculation Example

Per Unit Calculation Current   Proposed

Mileage Drain Interval A 15,000   45,000

Annual Miles per Unit B 135,000   135,000

Oil Changes per Unit per Year C 9.00   3.00

Crankcase Capacity (gallons) D 11   11

Gallons of New Oil per Unit per Year E 99.00   33.00

Per Gallon Cost of Oil F $10.00   $25.00

Annualized Oil Cost per Unit per Year G $990.00   $825.00

     

Oil Filter cost H $12.00   $12.00

Filter Change Interval I 15,000   15,000

Oil Filters per Unit per Year J 9.00   9.00

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Annualized Filter Cost K $108.00   $108.00

     

Hourly Labor Rate L $75.00   $75.00

Time Required for Oil Service M 0.50   0.50

Labor Cost per Oil Change N $37.50   $37.50

Annualized Oil Labor Cost O $337.50   $112.50

     

Time Required for Filter Change P 0.25   0.25

Labor Cost per Filter Change Q $18.75   $18.75

Annualized Filter Labor Cost R $168.75   $168.75

     

Used Oil per Unit per Year S 99.00   33.00

Per Gallon Oil Disposal Cost T $0.40   $0.40

Annualized Used Oil Disposal Cost U $39.60   $13.20

     

Oil Analysis Cost per Test V $15.00   $15.00

Oil Analysis per Unit per Year W 2   2

Annualized Oil Analysis Cost X $30.00   $30.00

     

Total Annualized Cost Per Unit Y $1,673.85   $1,257.45

Fleet Calculation  

Total Number of Units in FLEET Z 100   100

TOTAL Annualized Fleet Cost AA $167,385.00   $125,745.00

The calculations above should be compared for the various intervals considered and weighed against possible risks associated with longer drain intervals. All variables must be balanced and strict adherence to the OSI guidelines contained within this document when arriving at an optimized oil/filter service interval. In all cases, a conservative approach is recommended.

SECTION IV ENGINE OIL FUNCTION AND PROPERTIES

This section introduces characteristics of engine oil, including its function, manufacture, ways it is improved, and mechanisms that lead to its degradation. Though various oil options are described herein, the OSI process should only be applied using an oil approved by the original equipment manufacturer.

Engine oil—which is considered an engine’s life blood—performs many functions. Engine oil:

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• Lubricates and cleans key components• Provides additives to enhance performance• Suspends contaminants• Neutralizes acids and protects components from corrosive wear• Seals piston rings• Carries heat from internal engine parts to the oil cooler• Functions as a hydraulic fluid for various engine systems• May be used to increase fuel economy

There are two general types of base oils used in today’s engine oils: mineral and synthetic oils. They are substantially different in performance capabilities even though they must both meet the same American Petroleum Institutes’ (API) performance specifications.

Mineral OilsMost engine oils are petroleum-based mineral oils. Mineral oil is derived from crude oil by a series of processing steps that extract the desired range of fluids from crude oil and reduces undesirable constituents that may impede its performance. In all cases, the final engine oil product consists of a mixture of components.

Petroleum-based engine oils are further differentiated by the type of crude from which they are derived. These terms relate to the chemical structure of the base oil and the properties of these oils differ. Engine oils are made with paraffinic crude oils because these oils provide desired physical and chemical properties when operating in hotter environments. Viscosity of petroleum-based oils is controlled by distillation, which separates a variety of components into groups—known as viscosity fractions—that have similar size and weight. Each viscosity fraction itself consists of a mixture of many different compounds as well.

Synthetic OilsSynthetic oils refer to those base stocks which have been synthesized by chemical reaction to specific compounds. Since there is very little variation in the composition of synthetic oils, these oils have very precise properties.

Synthetics are characterized by the types of compounds that are combined together to form the oil. But since synthetics use specific compounds rather than mixtures of compounds, they are generally more expensive to manufacture.

Re-refined OilsA third source of base oils is through a re-refining process. In this case, used engine oil is collected, re-refined and additized into a usable product.

NOTE: Reclaiming and recycling processes are not the same as re-refining. The former attempts to remove undesirable constituents through settling or filtration processes.

During processing, solids and water are removed and the oil is distilled and hydro-treated. Oils collected for re-refining may be petroleum based or synthetic. The end result of an acceptable re-refining process is base oil that can be formulated to meet the targeted API performance specification. Currently, there is a limited volume of re-refined oils available.

ViscosityOne of the most important properties of an engine oil—whether it be synthetic or mineral based—is viscosity. Viscosity is a measure of a liquid’s resistance to flow. Viscosity varies with temperature; low-viscosity oil flows easily. A high-viscosity oil flows more slowly, is more resistant to shear loads and, thus, is able to carry higher loads. Generally, viscosity decreases as temperature increases.

There are two types of viscosity grades for engine oils: single-grade, and multi-grade. Single grade (or mono-grade) engine oils (e.g., SAE 30 or SAE 50) are primarily used in two-stroke diesel

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engines for film strength reasons. These oils are generally too viscous at low temperatures.

Multi-grade oils usually provide better fuel economy than single-grade oils. In addition, they exhibit several advantages over single-grade oils:

• Better low temperature startability• Faster oil flow to bearings at low temperature• Lower oil consumption• Higher viscosity at high temperature

Engine Oil Additive PackagesOriginal Oil Additive Packages—Engine oil is composed of a combination of base oils, performance additives, viscosity modifiers (if multi-grade) and pour point depressants. These components work together to provide the appropriate performance for the intended application.

How well these components work together is measured by a long-established process that tests, registers, licenses, and documents engine oil performance-developed jointly by the American Petroleum Institute (API), Society of Automotive Engineers (SAE), American Society of Testing and Materials (ASTM), American Chemistry Council (ACC) Petroleum Additive panel, American Automobile Manufacturers’ Association (AAMA), and Truck and Engine Manufacturers’ Association (TMA/EMA).

Oil classification is related to consumers via the “API Service Symbol” printed on the oil container. The use of the symbol or mark is described in API Publication 1509, “Engine Oil Licensing and Certification System (EOLCS).” Both gasoline and diesel engines are covered by these processes. Original product additive packages have been thoroughly tested and evaluated against their intended performance targets. This assures the consumer that the oil will perform as intended and will meet manufacturer specifications and warranty requirements.

Aftermarket/Supplemental Additive Packages—there are many aftermarket/supplemental oil additives produced to treat a variety of problems. The performance of these products are described by their manufacturers and are generally neither tested nor evaluated by the processes required for initial qualification of an engine oil.

Compatibility between aftermarket/supplemental additives and the original oil product is important. The performance of the original oil and any aftermarket products may differ when combined if the combination is not thoroughly tested.

Application of this RP assumes the user follows original equipment guidelines for selection of engine oil as well as aftermarket/supplemental engine oil additives, where approved. Unless specifically authorized for use by the engine and lubricant manufacturers it is not advised that aftermarket engine oil additives be used.

Reasons Why Engine Oil Must Be ChangedOil must be changed to remove contaminants that have been suspended in the oil, such as dirt, soot, water, acids, etc., and replenish additives which are an extremely important part of the engine oil package. Engine oil should be changed regularly to:

• Compensate for Viscosity Changes• Remove Suspended Solids• Remove Suspended Chemicals• Compensate for Chemical Changes• Replace Depleted Additives

See TMC RP 1403 for a thorough explanation on the importance of these five reasons.

NOTE: Extending an oil or filter beyond the engineered capability may result in accelerated wear and/or engine damage. This may necessitate a premature engine overhaul and may impact the engine warranty.

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This condition is not workmanship or material related, therefore, it would not be covered under most engine product warranties.

SECTION V EFFECTS OF ENGINE DESIGN AND CONDITION ON OIL LIFE

Within the engine, oil is stored in the oil pan, and pumped through a pressure regulator, cooler, filter, and drillings through which it is distributed to bearings, pistons, cooling nozzles, turbocharger and gear driven accessories.

In recent years, diesel fuel and engines have changed because of the need to reduce emissions to comply with EPA regulations. Changes in fuels and engine technologies have prompted changes in engine oil formulations as well as maintenance service intervals.

Different engine designs and EPA compliance vintages require different engine oil formulations, i.e. API CJ-4, CK-4, FA-4. Consult your engine manufacturer’s recommendations for specific oil requirements.

A manufacturer’s recommended oil change interval may not fully utilize the oil to its potential. Manufacturers may publish alternative methods for establishing optimum oil change intervals. These methods take into consideration a variety of factors including: sump capacity/oil contamination trends of the engine in a given environment, the amount of fuel consumed, overall duty cycle, and the amount of oil consumed.

Engine design and/or operating characteristics can affect oil service life. For example, if two engines are identical except for their engine oil capacity, the engine with the larger oil capacity can have a longer engine oil drain interval at a fixed contamination level. Similarly, if two engines are identical except for their contamination level (i.e. soot loading), the engine with the lower contamination level can have a longer engine oil life.

An engine’s mechanical condition affects oil service life. If the piston rings or valve guides are worn, then combustion by-products may accelerate oil additive depletion. If the engine is consuming some oil but not bypassing combustion by-products into the oil at excessive rates, oil service life may actually increase because additives are replenished by the higher amount of oil added between changes.

SECTION VI OIL FILTRATION

“Full Flow” FiltrationFilter performance is as critical as the oil performance. Selecting an OSI capable filter with the required durability and capacity is essential. A plugged or ruptured filter will quickly affect oil quality and cause potential damage to the engine. Regular duty cellulose element oil filters may not be suitable for extended drain applications. Many oil filter manufacturers now offer extended service filters. Please consult with the engine OEM and filter supplier.

The purpose of oil filtration is to protect the engine from contaminants such as soot and wear metals (typically in the 20-30 micron range). To this end, in modern diesel engine oil systems, 100 percent of the oil circulated in an engine is pumped through a “full flow” filter before it flows to the engine to lubricate and cool. Thus, they are called “full flow” filters.

Bypass FiltrationNot all engines use by-pass filtration, but when used, its purpose is to provide another option for the engine oil to be passed through to a finer (smaller micron) level of filtration. These bypass filters can be designed and built into the engine lubrication system or they can be added separate from the engine lubrication system. Not all engine OEMs support the use of by-pass filtration, consult with the engine OEM.

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Those that are mounted on the vehicle separate from the engine are typically connected by oil hoses. These hoses must be high-pressure, high-temperature, SAE approved hoses.

For engines equipped with bypass filters, a small portion, approximately 10 percent, of the oil flow is diverted to the bypass filter, which filters down to 5-10 microns. Since only a portion of the oil is filtered during each pass through a bypass filter, multiple passes are required to ensure that virtually all the oil is filtered. With most systems, essentially 100 percent of the oil is filtered every 20 to 30 minutes of engine operation. Some fleets use aftermarket add-on by-pass filtration. The fleet must weigh the cost of purchase, installation and future service of these products against any possible benefits.

Bypass filtration should not be confused with the action of the oil filter pressure relief valve, (also known as a by-pass valve) which when flow is restricted due to excessive oil viscosity or contamination, diverts oils so it bypasses the full flow filter, and continues to flow to the engine.

Supplemental Aftermarket Filtration EquipmentA wide variety of aftermarket systems and devices are available to replace or augment the oil filtration equipment provided by the original engine manufacturer. The applicability, cost, and represented benefits must be carefully evaluated, by fleets, through a controlled and documented test program. To measure the direct contribution in performance from these devices, fleets should test these devices against a set of “Control” trucks (by-pass filtration system disabled) and conduct a side-by-side comparison. Not all engine OEMs support the use of supplemental aftermarket filtration equipment, consult with the engine OEM.

Filter Operation And MaintenanceOil filters (cartridges and spin-ons) contain fibrous media to capture and retain contaminants filtered from the oil. Over time, the filter media can become plugged, restricting oil flow. Some fibrous media can also change properties over time if left in service too long. For these reasons, oil filters must be replaced periodically. Follow engine and/or filter manufacturer suggestions for appropriate filter change intervals for the targeted OSI intervals if different from the engine OEM recommendation.

Oil filters used in extended service intervals typically use more durable materials to ensure they stand up to the extended service life. Typically these material differences are contained in the media, potting compounds and seal materials to withstand the longer duration exposed to heat and contaminants.

Filtration and Engine WarrantyIt is recommended that the aftermarket filter or device include a product warranty for defects in the product. While engine manufacturers cannot “void” a user’s warranty or deny coverage merely due to the use of an aftermarket part, the engine manufacturers can reject warranty claims caused by defective aftermarket products.

CAUTION: As with all materials which could potentially harm the environment, prudent handling and legal disposal of used motor oil and spent oil filters is recommended and may be lawfully required. Be sure to follow all appropriate federal, state, and local regulations.

SECTION VIIOPERATING ENVIRONMENT

Oil condition and service intervals are adversely affected by operating environment extremes.

High TemperaturesExtreme heat can challenge a cooling system, particularly when operating in “stop-n-go” or slowed traffic, under load, and while operating accessories. Higher engine temperatures may accelerate oil deterioration and engine deposits which reduce engine life.

Cold Temperatures

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Cold starting is tough on engine oil, resulting in suspended moisture and reduced lubrication due to increased viscosity. In addition, allowing an engine to idle for long periods of time at low operating temperature may result in fuel dilution and/or increased engine deposits.

Airborne Dirt/DustThe presence of airborne dirt and the ability of the air cleaner system to filter it can affect oil performance and engine life. Compromised air intake systems and its components can allow additional abrasive particles to flow into the engine. Inertial air separators that are not maintained may become filled and create additional stress on the air intake system. Ensuring the proper maintenance of the air system to include the dust evacuator valve (boot) is an important part of optimized service intervals. Dirt will cause piston ring and cylinder wall deterioration as well as invade the oil reservoir. Once in the oil the dirt will be carried throughout the engine resulting in further damage and shorter oil filter life.

Cooling System RequirementsTo minimize the impact of extreme operating environments, the vehicle cooling system must have: good heat transfer capability, an open coolant flow path, healthy coolant chemistry, and unrestricted air flow for heat transfer. Any weakness in the cooling system can cause inadequate cooling, and higher engine temperatures, accelerating oil breakdown. Refer to your engine OEM and/or TMC RP365 for proper coolant system maintenance.

SECTION VIII DUTY-CYCLE CHARACTERISTICS

Heavy-duty diesel truck engines operate in three general categories:• Over-the road or on-highway• Local or city driving• Vocational/ off-highway

Each of these driving conditions may impact the engine oil/oil filter in a different way.

Frequent Stops and StartsFrequent stops and starts exert more performance demand on the engine oil. Any operation of this type with marginal engine oil performance can result in reduced engine life or catastrophic failure.

Extended IdlingEngine operation at low RPM with no load, particularly in cold weather, can be a major cause of excessive fuel dilution caused by unburned fuel passing beyond the piston rings. Higher fuel dilution may reduce oil viscosity and lower oil system pressure resulting in inadequate lubrication. (Lower engine operating temperature is another negative consequence of extended idling.)

Load Factor VariabilityMany times a diesel engine operates under varying load factors through its duty cycle. This can result in variable demand upon the engine cooling and lubrication system which, if not in good condition, can result in excessive heat stress, or cold operability, contributing to oil deterioration.

Fuel ConsumptionLoad factor variability can be measured by the amount of fuel consumed. Total fuel consumption may Be used to determine oil drain interval.

Sustained Highway OperationSteady engine operation will result in normal operating temperatures. This will provide maximum oil life. When operating under high stress engine conditions (i.e. mountainous/hilly terrains, heavy haul, etc.) the higher horsepower demand tends to raise the engine temperature above normal. High operating temperatures may shorten oil life expectancy due to accelerated oil oxidation/thermal decomposition.

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SECTION IXDRIVER OPERATING FACTORS

Many professional drivers are not aware that some of their driving habits adversely affect engine and oil life. In general, anything that adversely affects fuel economy will also affect engine and oil life. Some of the driving methods which negatively impact engine oil performance include:• Extended Idling - (See Section VI, Duty- Cycle Characteristics)• Lugging - Engine operation below the engine manufacturers recommended minimum full load RPM can

result in excessive lube oil deterioration due to soot buildup or high oil temperature.• High Engine Speed – sustained operation at rpms exceeding rated engine speed can result in excessive

lube oil deterioration due to soot buildup and stress on the after-treatment system.• Hot Shutdown - Instant shutdown after a sustained period of maximum load at high temperature can

result in hot spots which can reduce oil service life. A brief period (more than 1 minute) of idling is recommended after full power operation.

• Improper Shift and Clutch Technique - Lugging and over speeding can often be caused by inadvertent clutch and shift action due to poor technique and training.

• Improper Gear Selection – sustained operation in a gear that is not optimal for fuel economy, can result in prolonged high speed engine operation (see High engine speed above).

• Performing Unnecessary Stationary Regenerations – when possible, an after-treatment regeneration should be managed over the road during the course of normal operation. Only in cases of low speed, light load operation, should a proactive stationary regeneration be conducted. Failure to do so can result in excessive lube oil deterioration due to soot buildup or higher oil temperature.

SECTION X USED ENGINE OIL ANALYSIS

An effective used oil analysis (UOA) program is the best method for determining optimized oil service life. A reliable UOA program consists of a series of standardized tests that are performed on the oil sample by the laboratory. The results of these tests, when compared against one another over time, reveal lubricant condition, contamination levels, and wear rates of oil-lubricated components present at the time the unit was sampled.

The oil analysis program is used to assess the health of the oil and engine during the period of time the oil was installed and in use. It’s critical that the proper tests are selected, proper sampling procedures are followed, sample label information is filled out completely and accurately, and valid testing procedures are followed. Refer to TMC RP 318B for additional information concerning used engine oil analysis. The sampling method and oil sample labeling are as critical to the process as the analytical testing. The following guidelines should be incorporated in the OSI process:

Use care to take the most representative oil samples:• Never sample a cold system - take sample after system has been warmed up and has reached

normal operating temperatures• When taking an interim sample, secure sample prior to adding "make-up oil"• Use same location and technique each time the system is sampled – engine oil sampling valves are

the preferred sampling method• Sample at pre-established frequencies (i.e. ±10% of the targeted sampling interval)• Flush sampling devices before taking the final sample• Ensure that you use only new and clean sample bottles • Visually examine sample for abnormalities prior to mailing to lab. Alert appropriate maintenance

personnel of any unusual conditions noticed (gross contamination, off-color e.g. milky, etc.)• Properly label sample and send to lab ASAP preferably using shipping that is trackable

Each sample label should include the following information:• Vehicle number, unit asset number, or ID number• Miles on engine since new or overhaul• Mileage on the oil since the last time the fluid was changed• Date the unit was sampled

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• Amount of make-up oil added since the last time the unit was sampled (Please ensure that make-up oil is added after taking the oil sample)

• Indicate whether or not the oil was drained at the time the sample was taken• Indicate whether or not the filter was changed at the time the sample was taken• Completely and correctly identify the fluid product manufacturer, fluid name and viscosity grade of

the oil sampled• Identify the engine manufacturer and model and serial number

Using elemental Analysis testing will help provide information on wear metals, contaminants and additives present in the lubricant. With this testing type and severity of wear can be determined as well as the severity of contamination. With trending history, elevated wear can pinpoint a specific area earlier than traditional methods. The chart below will help explain the possible sources for the typical metals found in your analysis results.

Wear Metals Possible Sources

Iron (Fe) Cylinder liners, rings, gears, crankshaft, camshaft, cast ironChrome (Cr) Rings, liners, exhaust valves, stainless steel alloyAluminum (Al) Pistons, thrust/cam/main/rod bearings, charge air cooler brazing fluxNickel (Ni) Alloy in valves, crankshaft, camshaft, and EGR Coolers Copper (Cu) Main/rod bearings, brass/bronze bushings, oil cooler core tubingLead (Pb) Overlay metal in main/rod bearings, sometimes solder, aftermarket additiveTin (Sn) Bearings, bronze bushings, flashing from pistons, solder from tin-lead solderCadmium (Cd) Environmental contaminant

Titanium (Ti) Valves, piston pins, bearings, shafts, possible engine oil additiveVanadium (V) Alloy metal,

Contaminant Metals

Possible Sources

Silicon (Si) Dirt (Silica), silicone from silicon based synthetic, silicon sealants, Silicates from antifreeze

Sodium (Na) Antifreeze (coolant leak)Potassium (K) Spray wash, antifreeze (coolant leak), additive from potassium borate gear oil,

charge air cooler brazing flux (turbocharged engines)

Multi-Source Metals

Possible Sources

Molybdenum (Mo) Additive in engine oils and molybdates from coolant leakAntimony (Sb) Alloy metal in Babbitt bearings, bushings, trace element used in some oilsManganese (Mn) Steel alloy metal in gears, some shafts

Additive Metals Possible Sources

Boron (B) Additive common in engine oils, some gear oilsMagnesium (Mg) Detergent/dispersant additive, alloy, environmental contaminantCalcium (Ca) Detergent/dispersant additive, water contamination, lime dust

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Barium (Ba) Not commonly found in engine oilsPhosphorus (P) Anti-wear additive ZDDP, phosphate ester, inhibitor found in antifreezeZinc (Zn) Alloy in brass, anti-wear additive ZDDP, galvanized steel from filter canisters

When determining optimized oil drain service intervals; the equipment and lubricant information must be identified and provided to the laboratory. The following testing may be performed by the laboratory to help determine equipment and lubricant health (for diesel engines) to safely optimize oil drain intervals. The following tests are essential when attempting to determine if the oil is suitable for continued use:

Elemental Metal Analysis Viscosity Base Number Oxidation/Nitration Soot Water % Fuel Dilution

Test Purpose/AffectElemental Metals Analysis

Check for equipment wear, contamination, and lubricant additives

Viscosity Confirm that the proper grade of oil is in use and within acceptable limits. Improper viscosity could increase engine wear.

Base Number

Measures the lubricants ability to neutralize acids. Excessive acids will increase engine component wear and corrosion.

Oxidation Excessive oxidation will prevent additives from performing properly and will determine if the lubricant is breaking down due to extended use or abnormal operating conditions.

Nitration Will indicate excessive “blow-by” gasses coming from the combustion chamber and passing the piston rings.

Soot Excessive soot may indicate reduced combustion efficiency and may cause the oil to thicken reducing the oils ability to flow properly. Soot may be abrasive and can result in excessive wear of internal components.

Water Percent

When present in the oil in larger quantities the result is a reduction of the lubricants ability to properly lubricate critical internal components.

Fuel Dilution

Amount of raw, unburned fuel that passes the piston rings and ends up in the crankcase. Excessive amounts will cause viscosity to lower reducing fluid film strength.

Establishing limits for the equipment and lubricant is helpful. A new baseline reference of the targeted lubricant will provide a baseline of the new lubricant and assist in establishing the limits for the fluid properties. The used lubricant will be compared to the baseline lubricant to help determine lubricant health and help with trending the results.

Monitoring equipment on regular sampling intervals will help to provide timely knowledge of an equipment issue. This allows the operator or maintenance person to react in a timely manner preventing unnecessary damage. Trends will be easier to spot and the appropriate action to take more clear. Most laboratories will utilize both statistical analysis and rate of change when defining abnormal wear.

Two main methods may be used for evaluating used oil analysis test results (1) accumulation and (2) rate of change. The accumulation approach (results taken directly from the used oil analysis report) assumes that the longer the oil is left in service the higher the accumulation for test results based upon concentration levels (i.e. wear metals). The higher accumulation of wear metals does not necessarily mean that wear is being induced. If the wear remains linear it may simply indicate that the engine is generating wear at the same rate and the elevated wear levels are due to their accumulation over a longer period of time.

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Using the rate of change approach helps to show at what point along the OSI the durability of the engine has become compromised or when the rate at which the engine generates wear increases (changes). For example, the rate-of-change method can be used to describe the parts per million of wear an engine generates every 10,000 miles (Fe, ppm/10,000 miles). When the rate of wear stays constant along the OSI, the process is indicating it’s operating within capability of supporting the extended service intervals without compromising engine durability.

Most oil analysis laboratories do not have condemning wear limits beyond the “standard” service intervals. Due to the accumulation factor of wear metals, the following guidelines may be used to assess the upper wear limits for extended service intervals when interim sampling and the statistical approach was used to set the OSI. When the final OSI has been validated several times and the statistical method used to factor in a margin of safety, as described in Section II, for datasets that are assumed to be normally distributed (i.e. bell curve):

• Calculate the average and standard deviation for the dataset of each of the engine wear metals• The dataset average plus one standard deviation can be used to calculate the value which falls

within 68% of all values in the data set. This may be used as a warning limit for future test results.

• The dataset average plus two standard deviations is used to calculate the value which falls within 95% of all values in the data set. This value may be used to flag an abnormal value for future test results.

NOTE: Statistics should be used on a larger sample size to increase the confidence level of the data. Smaller OSI projects will generate less data during the testing phase so in order to increase the confidence level of the dataset it seems practical to either run more testing intervals or add more test trucks, or to continue to include on-going data to the sample population or a combination of all of these.

SECTION XISUMMARY AND CONCLUSION

The optimized service intervals holds potential opportunity for true maintenance cost savings. Service intervals extended beyond engine OEMs recommendations must be tempered with an understanding of the discipline required to conduct the OSI, and the potential risks therefore. The following recommended practices; TMC RP 1403, and TMC RP 318, offer considerations and trade-offs which fleets should consider when extending drain intervals.

Optimum service intervals must be decided upon with concern for the other components and systems of the vehicle. Such items as transmissions (standard and/or automatic), differentials, axles, wheel bearings, suspensions, tire pressure and condition, cooling system, brake condition, lighting, safety, and many other components/systems, must be able to be performed at or in sync with the targeted OSI. If the servicing of any system or component cannot be synced with the oil/oil filter optimum service interval, it must be serviced independently or replaced with a capable substitute.

An optimum service interval study is a 'snapshot' in time for the existing fleet to operate at the OSI. Changes in the fleet's operation or make-up (i.e. engine make/model, EPA vintage, etc.) may require re-validating the OSI. New engine hardware changes, often driven by emissions regulations, can affect lubricant and/or filter performance. Changes to maintenance practices or operating conditions can have similar effects. Participation in a regular used oil analysis program will allow the fleet to continually monitor their equipment and reassess their maintenance practices as the aforementioned changes take place.

NOTE: All parties involved in the OSI program need to understand the risks and rewards of undertaking an OSI approach. The parties involved should have practical experience in an OSI, in vehicles of similar; make/model, EPA vintage, application, duty cycles and service interval(s) as those being evaluated by the fleet. The user needs to understand their responsibilities and to provide required documentation (i.e. used

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oil analysis results, frequency of drains/sampling, oil/oil filter brand used and maintenance records) for consideration of warranty reimbursement.

REFERENCESFor more information about lubricant fundamentals, extending oil drain intervals in light- and medium-duty engines, and used engine oil analysis, refer to:

TMC RP 318C, Used Engine Oil Analysis TMC RP 624A, Lubricant Fundamentals TMC RP 1403, Determining Engine Oil Change Intervals For Light-and Medium Duty Vehicles TMC RP 1417, Lubricant and Fluid Sampling Guidelines TMC RP 1420, Fluid Analysis for Class 2-6 Vehicles TMC RP 365, Coolant Maintenance Guidelines

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