1998 Lexus ES 300 Owners Manual - Page 197

ENGINE 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. D 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 gases during the combustion process. D 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. The amount of engine oil consumed depends on the viscosity of the oil, the quality of the oil and the way the vehicle is driven. More oil is consumed under driving conditions such 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, keep in mind that the oil may have become diluted, making it difficult to judge the true level accurately. For 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 because 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. Lexus recommends that the oil level be checked every time you refuel the vehicle. NOTICE Failure to check the oil level regularly could lead to serious engine trouble due to insufficient oil. For detailed information on oil level check, see "Checking the engine oil level" on page 198. 197