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.
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.
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 conditions
the vehicle is driven under.
More oil is consumed by high- speed
driving 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 that 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 because the
oil is gradually becoming diluted with
fuel or moisture, making it appear that
the oil level has not changed.
