FUNCTIONS OF ENGINE OIL
Engine oil has the primary functions of lubricating and cooling the inside of the engine, and plays a major role in maintaining the engine in proper working order.
ENGINE OIL CONSUMPTION
It is normal that an engine should consume some engine oil during normal engine operation. The causes of oil consumption in a normal engine are as follows.
The amount of engine oil consumed depends on the viscosity of the oil, the quality of the oil and the conditions the vehicle is driven under.
- Oil is used to lubricate pistons, piston rings and cylinders. A thin film of oil is left on the cylinder wall when a piston moves downwards in the cylinder. High negative pressure generated when the vehicle is decelerating sucks some of this oil into the combustion chamber. This oil as well as some part of the oil film left on the cylinder wall is burned by the high temperature combustion gasses during the combustion process.
- Oil is also used to lubricate the stems of the intake valves. Some of this oil is sucked into the combustion chamber together with the intake air and is burned along with the fuel. High temperature exhaust gases also burn the oil used to lubricate the exhaust valve stems.
More oil is consumed under such driven conditions as high speeds and frequent acceleration and deceleration.
A new engine consumes more oil, since its pistons, piston rings and cylinder walls have not become conditioned.
When judging the amount of oil consumption, note the oil may become diluted and make it difficult to judge the true level accurately.
As an example, if a vehicle is used for repeated short trips, and consumes a normal amount of oil, the dipstick may not show any drop in the oil level at all, even after 1000 km (600 miles) or more. This is beacuse the oil is gradually becoming diluted with fuel or moisture, making it appear that the oil level has not changed.
The diluting ingredients evaporate out when the vehicle is then driven at high speeds, as on an expressway, making it appear that oil is excessively consumed after driving at high speeds.
IMPORTANCE OF ENGINE OIL LEVEL CHECK
One of the most important points in proper vehicle maintenance is to keep the engine oil at the optimum level so that oil function will not be impaired. Therefore, it is essential that the oil level be checked regularly. Toyota recommends that the oil level be checked every time you refuel the vehicle.
Failure to check the oil level regularly could lead to serious engine troubles due to insufficient oil.
For detailed information on oil level check, see Checking the Engine Oil Level.