Oil Consumption Diagnosis

Engine Mechanical - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 2370748 Explanation

Note

Oil consumption for a combustion engine refers to the amount of oil consumed as a result of the combustion process. Oil consumption is not to be equated with oil loss resulting from leaks from components such as the oil pan and cylinder head cover. The role of the engine oil is to:

1. Separate surfaces that slide against each other by means of an oil film, i.e. to prevent dry friction.
2. Dissipate heat generated by friction.
3. Lead away combustion residue. This task involves the consumption of a certain amount of oil. It is therefore wrong to assume that future enhancements of the combustion engine may produce an engine which has zero oil consumption. Outside operating conditions, driving style and manufacturing tolerances do, however, have an impact on oil consumption. It is imperative that oil be filled when the level has fallen below the “MIN” mark on the dipstick. It is also important to ensure that the oil level is not above the “MAX” mark on the dipstick as this could result in increased oil consumption. As oil consumption is affected by technical factors, the conclusion is reached that the engine does not consume oil in special operating conditions that lead to oil dilution. During conditions such as frequent cold starts and driving before the engine reaches operating temperature, it is only the oil flowing back to the oil pan that carries away scalding fuel components and precipitates. This “dilutes” the oil and leads to the erroneous assumption that the engine consumes no oil. Such diluted oil loses its ability to lubricate and could cause engine damage if the prescribed oil change intervals are not observed. Driving in predominately urban traffic and frequently running a cold engine at rpms above idle speed are the main causes of oil dilution. As oil consumption does not stabilize until after a few thousand kilometers of travel, oil consumption measurements are not reliable until after a distance of about 7,500 km. The oil standard is merely used for monitoring and cannot be used for measurement purposes. In principle, the engine must have stopped for at least 5 minutes or 10 minutes before checking the oil level. If the maximum amount of oil added during an oil change does not agree with the max. on the oil dip stick, then this will be accounted for by the necessary manufacturing tolerances. Meassuring Procedure

Note

All information on permissible engine oil consumption and capacities are found in the Owner’s Manual.

1. Before measuring consumption, ensure that the engine is not losing oil due to leakage.
2. The check is carried out with the vehicle parked on a level surface with the engine at operating temperature (engine oil temperature at least 80 °C).
3. Drain the engine oil immediately after switching off the engine - drainage time = approx. 30 minutes (this value has been obtain through technical trials).
4. The quantity of drained engine oil is determined via a measuring container. The container is then filled with fresh oil up to the maximum engine oil capacity minus the volume remaining in the unchanged oil filter.
5. With this engine oil quantity, the customer should be able to travel at 1000 km without needing to top up engine oil (the distance profile and customer driving style should be maintained).
6. Then, the preceding procedure (points 1 and 2) should be repeated with the exact same engine drainage time.
7. The oil quantity now “missing” from the measuring container is equal to the engine oil consumption for that distance.
8. Oil consumption is calculated as follows: (filled oil quantity (l) – drained oil quantity (l)) / total distance driven (km) x 1000 = oil consumption (l/1000 km)