4RUNNER (1998)
Keep the back door and back
window closed while driving. An
open or unsealed back door and
back window, may cause ex-
haust gases to be drawn into
the vehicle. If you must drive
with the trunk lid open to ac-
commodate a large object, close
the windows, open all the
instrument panel vents and
have the heating or cooling sys-
tem deliver fresh air into the
vehicle by turning the fan to
high speed with the air intake
control set at the outside air
position.
To allow proper operation of
your vehicle's ventilation sys-
tem, keep the inlet grilles in
front of the windshield clear of
snow, leaves, or other obstruc-
tions.
If you smell exhaust fumes in
the vehicle, drive with the win-
dows open and the back door
and back window closed. Have
the cause immediately located
and corrected.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 work-
ing 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 nor-
mal 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 down-
wards in the cylinder. High nega-
tive 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 cylin-
der wall is burned by the high tem-
perature 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 com-
bustion 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 condi-
tions 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 cyl-
inder walls have not become condi-
tioned.
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.
Facts about engine oil
consumption
