Oil Consumption

NOTE: Use the following information to assist in explaining "normal" oil consumption to vehicle owners.

DESCRIPTION
Break-In Period
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 16,000 kilometers (10,000 miles), when a new engine is being "broken in" or until certain internal engine components become conditioned.

Severe Service
Vehicles used in heavy duty operation (severe service) may use more oil. The following applications are examples of heavy duty operation:
^ Trailer towing or severe loading.
^ Taxi cab or police service.
^ Sustained high speed operation.

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

Oil Consumed
When the pistons move downward, a thin film of oil is left on the cylinder walls. This thin film of oil is burned away on the firing stroke during combustion. Efficient engines will use some oil or they would quickly wear out. As the vehicle is operated, some oil is drawn into the combustion chambers past the intake and exhaust valve stem seals and burned. For an efficient engine, the amount of oil lost or burned is minimal. If an engine burned 1 drop of oil during each firing stroke, oil consumption would be about 1 Liter (1 quart) for every kilometer (mile) traveled. Fortunately, modern engines use much less oil than this example.

Consumption Rate
Vehicles in normal service should get at least 1450 kilometers (900 miles) per quart after 16,000 kilometers (10,000 miles) of service. Several conditions can affect oil consumption rates. The following is a partial list of these items:
^ Engine size.
^ Operator driving habits.
^ Ambient temperature.
^ Quality and viscosity of the oil.

Misleading Information
Operation under varying conditions can frequently be misleading. A vehicle that has been run for several thousand kilometers (miles) of short trip operations or 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 dipstick 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 oil is checked, it may appear that a quart of oil was used in 160 kilometers (100 miles). This perceived 160 kilometers (100 miles) per quart consumption rate causes customer concern even though the actual oil consumption rate was about 2,400 kilometers (1,500 miles) per quart.

Oil Viscosity and Rating
Make sure the selected engine oil meets the recommended API performance category "SG" and SAE viscosity grade as shown in the vehicle's Owner Guide. It is also important that the engine oil is changed at the intervals specified for the typical operating conditions of the vehicle. This information is available in the Owner Guide, Maintenance Schedule and Record Log.

PRE-CHECKS
1. Determine what is considered excessive oil consumption (i.e., how many miles are driven per quart of oil). Also, determine the owner's driving habits, (i.e., sustained high speed operation, towing, extended idle, etc.). Oil usage is normally greater during the first 16,000 kilometers (10,000 miles) of service. As mileage increases, oil usage generally decreases. Vehicles in normal service should get at least 1450 kilometers (900 miles) per quart after 16,000 kilometers (10,000 miles) of service. High speed driving, towing, high ambient temperature, etc. may result in greater oil usage.
2. Verify engine has no external oil leak. Refer to Engine Oil Leaks.
3. Verify engine has correct oil level dipstick.
4. Verify that the engine is NOT being run in an overfilled condition. Check the oil level at least 5 minutes after a hot shutdown with the vehicle parked on a level surface. In no case should the level be above the "F" mark. If a significant overfill is indicated, perform Oil Consumption Test steps 1 through 4.
5. Perform an oil consumption test.

OIL CONSUMPTION TEST
1. Drain engine oil, replace the oil filter and refill with 1 Liter (1 quart) LESS than the recommended oil.
2. Run the engine for 3 minutes (10 minutes if cold). Shut OFF engine, then allow oil to drain to oil pan for at least 5 minutes with vehicle on level surface.
3. Remove oil level dipstick and wipe clean. (Do not wipe with anything contaminated with silicone compounds). Install oil level dipstick being sure to seat the oil level dipstick firmly seated in the oil level indicator tube. Remove the oil level dipstick and scribe a mark on the back (unmarked) surface at the indicated oil level. (This level should be about the same as the "L" mark on the face of the oil level dipstick.)
4. Add 1 Liter (1 quart) of oil. Start the engine and allow to idle for at least two minutes. Shut OFF the engine and allow oil to drain to oil pan for at least 5 minutes. Mark the oil level dipstick using the procedure above. (This level may be slightly below the "F" mark.)
5. Record the vehicle's mileage.
6. Instruct the owner to drive the vehicle as usual and:
(1) Check the oil level regularly at intervals of 160 to 240 km (100 to 150 miles).
(2) Return to the service point when the oil level drops below the "L" mark on the oil level dipstick.
(3) In an emergency, add only full 1 Liter (1 quart) bottles of the same oil and note the mileage at which the oil is added.
7. Check the oil level under the same conditions and at the same location as in Steps 3 and 4 above.
(1) Measure the distance from the oil level to the UPPER scribe mark on the oil level dipstick and record.
(2) Measure the distance between the two scribe marks and record.
(3) Divide the first measurement by the second.
(4) Divide the distance driven during the oil test by the result. This quantity is the approximate oil consumption rate in Kilometers Per Liter (KPL) or, Miles Per Quart (MPQ).
8. If the oil consumption rate determined is unacceptable, proceed to Diagnosis.

DIAGNOSIS
1. Check Positive Crankcase Ventilation (PCV) system. Make sure the system is not plugged.
2. Check for plugged oil drain-back holes in the cylinder heads and cylinder block.
3. If, after performing the above, the condition still exists, proceed to Step 4.
4. Perform the Compression Test, and/or perform a Cylinder Leakage Detector Test. This can be helpful in determining source of oil consumption (e.g., valves, piston rings).

NOTE: After checking for worn parts, if it is determined parts should be replaced, make sure correct replacement parts are used.

5. Check valve guides for excessive guide clearance. Replace all valve stem seals after verifying valve guide clearance.
6. Worn or damaged internal engine components can cause excessive oil consumption. Small deposits of oil on tips of spark plugs can be a clue to internal oil consumption. If internal oil consumption still persists, proceed as follows:
a. Remove the engine from the vehicle and place it on an engine work stand. Remove the intake manifolds, cylinder heads, oil pan, and oil pump.
b. Check the piston ring clearance, ring gap, and ring orientation. Service as required.
c. Check for excessive main bearing clearance. Service as required.
7. Repeat the test to verify the concern has been repaired.