Toyota Prius Owners Manual
Facts about engine oil consumption
FUNCTIONS OF ENGINE OIL
Engine oil has the primary functions oflubricating and cooling the inside of theengine, and plays a major role in maintainingthe engine in proper working order.
ENGINE OIL CONSUMPTION
It is normal that an engine should consumesome engine oil during normalengine operation. The causes of oilconsumption in a normal engine are asfollows.
Oil is used to lubricate pistons, pistonrings and cylinders. A thin film of oilis left on the cylinder wall when apiston moves downwards in the cylinder.High negative pressure generatedwhen the vehicle is decelerating suckssome of this oil into the combustionchamber. This oil as well as some partof the oil film left on the cylinder wallis burned by the high temperature combustiongases during the combustionprocess.
Oil is also used to lubricate the stemsof the intake valves. Some of this oilis sucked into the combustion chambertogether with the intake air and isburned along with the fuel. High temperatureexhaust gases also burn theoil used to lubricate the exhaust valvestems.
The amount of engine oil consumed dependson the viscosity of the oil, thequality of the oil and the conditions thevehicle is driven under.
More oil is consumed by high−speed drivingand frequent acceleration and deceleration.
A new engine consumes more oil, sinceits pistons, piston rings and cylinder wallshave not become conditioned.
Oil consumption: Max. 1.0 L per 1000km (1.1 qt./600 miles, 0.9 Imp.qt./600miles)
When judging the amount of oil consumption,note that the oil may becomediluted and make it difficult to judgethe true level accurately.
As an example, if a vehicle is used forrepeated short trips, and consumes a normalamount of oil, the dipstick may notshow any drop in the oil level at all, evenafter 1000 km (600 miles) or more. Thisis because the oil is gradually becomingdiluted with fuel or moisture, making itappear that the oil level has not changed.
The diluting ingredients evaporate outwhen the vehicle is then driven at highspeeds, as on an expressway, making itappear that oil is excessively consumedafter driving at high speeds.
IMPORTANCE OF ENGINE OIL LEVELCHECK
One of the most important points in propervehicle maintenance is to keep the engineoil at the optimum level so that oilfunction will not be impaired. Therefore, itis essential that the oil level be checkedregularly. Toyota recommends that the oillevel be checked every time you refuelthe vehicle.
Failure to check the oil level regularlycould lead to serious engine troubledue to insufficient oil.
For detailed information on oil level check,see “Checking the engine oil level” onpage 404.