Lexus ES-300 2001 Manual page 424

FACTS ABOUT ENGINE OIL
CONSUMPTION
Functions of engine oil
Engine oil has the primary function 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.
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.
ENGINE
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