Oil - Normal Oil Consumption
File In Section: 6 - EngineBulletin No.: 18-61-03
Date: October, 1995
INFORMATION
Subject:
Oil Economy
Models:
All Passenger Cars and U Vans
This bulletin is being revised to update models and to revise text. Previous divisional publication number was:
GM Canada 92-6-102
We have received dealer requests for information they may use to advise owners what is considered normal oil consumption in today's engines. What normal oil consumption is, can best be answered if specific driving conditions to which a car is subjected are known. It is similar to asking what is the normal fuel economy for any given model. There are many variables involved in determining acceptable oil consumption; therefore, a simple specific statement can not be offered.
Oils recommended for your vehicle can be identified by looking for the "Starburst" symbol. This symbol indicates that the oil has been certified by the American Petroleum Institute (API)>. Do not use any oil which does not carry this Starburst symbol. (Figure 1)
If you change your own oil, be sure you use oil that has the Starburst symbol on the front of the oil container.
If you have your oil changed for you, be sure the oil put into your engine is American Petroleum Institute certified for gasoline engines.
You should also use the proper viscosity oil for your vehicle, as shown in the following chart: (Figure 2) As shown in the chart, if you have the 3.1L engine, SAE 5W-30 is best for your vehicle. However, you can use SAE 10W-30 if it's going to be 0° F (-18° C) or above. These numbers on an oil container show its viscosity, or thickness. Do not use other viscosity oils, such as SAE 20W-50.
The following information is in agreement with our Engineering Department, and since it is a down-to-earth reply, we are hopeful that it will be useful in answering owners' inquiries concerning oil consumption for all size engines used in today's products. Along with this information is a list of possible causes for increased oil consumption which is published in Section 6 of all 1991 Pontiac service manuals. Reference this information when all concerns mentioned in the following reply have been addressed.
"A gasoline engine depends upon oil to lubricate the cylinder walls, pistons and piston rings. When the piston moves downward, a thin film of oil is left on the cylinder walls and on the firing stroke it is burned by the flame combustion. For example, if an engine were to burn as much as one drop of oil every firing stroke, then it would use more than one quart every two miles. Modern engines use much less oil than one drop, but all efficient engines use some oil. If they did not, they would quickly wear out."
The rate of oil consumption depends upon engine sizes, the quality and viscosity of the oil, the speed at which the engine is operated, the temperature and the amount of dilution and oxidation which takes place. These conditions are frequently misleading. As an example, a car that has run 1,000 miles or more in city operation may have consumed a normal amount of oil, yet actually measures up to the full mark due to dilution (condensation and fuel) in the crankcase. The car then might be driven at higher speeds on the highway; the dilution elements boil off and the car appears to have used two quarts of oil in a hundred miles.
Important:
Importance of changing the oil. As the preceding paragraph discusses flame combustion and oil consumption; the reverse of the process can take place. Combustion by-products can be deposited in the oil causing the oil level to stay at or near the full mark on the dipstick, but the oil is diluted.
"Car owners should expect increased oil consumption at high speeds. No standard rate of consumption can be established because under various combinations of the engine sizes and conditions mentioned above, one engine might use a quart in 2,500 miles and another use a quart in 1,500 miles and yet both engines might be normal."
"New engines require considerable running time before the piston rings and cylinder walls become 'conditioned' and during this time they use oil more rapidly than later. Typically, an engine's oil economy should not be judged until it has run at least 4,000 miles."
Also, improper methods of checking oil level may lead a customer to believe that their vehicle has excessive oil consumption. Check oil on a level surface, engine off and at operating temperature. Allow adequate time for the oil to drain back into the oil pan.
Keeping the above information in mind, be certain that the customer is using the oil recommended in the Owner's Manual. Always use an oil which is American Petroleum Institute (API) certified for use in gasoline engines, and which displays the API certification mark (Starburst Symbol). Also, always use an oil of proper viscosity as specified in the vehicle's Owners Manual.
While normal oil consumption varies, we believe the use of 2 quarts (1.9L) or more of engine oil within 2,000 miles or 3,200 kilometers should be cause for investigation. Address the following items to determine the source of the oil consumption.
^ External oil leaks. Perform OIL LEAK DIAGNOSIS found in Service Manual, Section 6.
^ Oil leaking into the cooling system via a cracked engine block. Check radiator for the presence of engine oil.
^ Crankcase ventilation system malfunction.
^ Valve guides and/or valve seals worn or seals omitted.
^ Piston rings broken, improperly installed, worn or not seated.
^ Piston improperly installed or misfitted.