Oil Consumption Test

Oil Consumption Test

The amount of oil an engine uses will vary with the way the vehicle is driven in addition to normal engine-to-engine variation. This is especially true during the first 16,100 km (10,000 miles) when a new engine is being broken in or until certain internal components become conditioned. Vehicles used in heavy-duty operation may use more oil. The following are examples of heavy-duty operation:
^ Trailer towing applications
^ Severe loading applications
^ Sustained high speed operation

Engines need oil to lubricate the following internal components:
^ Cylinder block cylinder walls
^ Pistons and piston rings
^ Intake and exhaust valve stems
^ Intake and exhaust valve guides
^ All internal engine components

When the pistons move downward, a thin film of oil is left on the cylinder walls. As the vehicle is operated, some oil is also drawn into the combustion chambers past the intake and exhaust valve stem seals and burned.

The following are examples of conditions that can affect oil consumption rates:
^ Engine size
^ Operator driving habits
^ Ambient temperatures
^ Quality and viscosity of oil
^ Engine is being run in an overfilled condition (check the oil level at least five minutes after a hot shutdown with the vehicle parked on a level surface. The oil level should not be above the top of the cross-hatched area and the letter "F" in FULL).

Operation under varying conditions can frequently be misleading. A vehicle that has been run for several thousand miles on short trips or in below-freezing ambient temperatures may have consumed a "normal" amount of oil. However, when checking the engine oil level, it may measure up to the full mark on the oil level indicator due to dilution (condensation and fuel) in the engine crankcase. The vehicle then might be driven at high speeds on the highway where the condensation and fuel boil off. The next time the engine oil is checked it may appear that a liter of oil was used in about 160 km (100 miles). Oil consumption rate is about one liter per 2,400 km (1,500 miles).

Make sure the selected engine oil meets manufacturer specification and the recommended API performance category "SG" and SAE viscosity grade as shown in the vehicle Owner's Guide. It is also important that the engine oil is changed at the intervals specified for the typical operating conditions.

The following diagnostic procedure is used to determine the source of excessive oil consumption.

NOTE: Oil use is normally greater during the first 16,100 km (10,000 miles) of service. As mileage increases, oil use decreases. High speed driving, towing, high ambient temperature and other factors may result in greater oil use.

1. Define excessive consumption, such as the number of miles driven per liter of oil used. Also determine customers driving habits, such as sustained high speed operation, towing, extended idle and other considerations.
2. Verify that the engine has no external oil leaks as described under Engine Oil Leaks in this section.
3. Carry out an oil consumption test:
^ Run the engine to normal operating temperature. Switch engine OFF and allow oil to drain back for at least five minutes.

Run the engine to normal operating temperature. Switch engine OFF and allow oil to drain back for at least five minutes.
^ With vehicle parked on level surface, check the engine oil level.

With vehicle parked on level surface, check the engine oil level.
^ If required, add engine oil to set level exactly to the FULL mark.

If required, add engine oil to set level exactly to the FULL mark.
^ Record the vehicle mileage.

Record the vehicle mileage.
^ Instruct the customer to return for a level check after driving the vehicle as usual for 1,610 km (1000 miles).

Instruct the customer to return for a level check after driving the vehicle as usual for 1,610 km (1000 miles).
^ Check the oil level under the same conditions and at the same location as the initial check.

Check the oil level under the same conditions and at the same location as the initial check.

NOTE: If the oil consumption rate is unacceptable go to Step 4.

4. Check the Positive Crankcase Ventilation (PCV) system. Make sure the system is not plugged.
5. Check for plugged oil drain-back holes in the cylinder head and cylinder block.
6. Carry out a cylinder compression test. Refer to the Compression Test procedure. Compression Test This can help determine the source of oil consumption such as valves, piston rings or other areas.
7. Check valve guides for excessive guide clearance. Install new valve stem seals after verifying valve guide clearance.
8. Worn or damaged internal engine components can cause excessive oil consumption. Small deposits of oil on the tips of the spark plugs can be a clue to internal oil consumption.