My 1996 olds. aurora keeps
Hello,
There are several problems that could be leading to an engine overheating. I will discuss some of them and you can try to act on which solutions that can help.
THERMOSTAT STUCK SHOT
The thermostat, which is usually located in a housing where
the upper radiator hose connects to the engine, controls the operating
temperature of the engine. It does this by blocking the flow
of coolant from the engine to the radiator until the engine reaches
a certain temperature (usually 190 to 195 degrees F.). When this
temperature is reached, the thermostat opens and allows coolant
to circulate from the engine to the radiator.
If the thermostat fails to open, which can happen due to mechanical
failure or if a steam pocket forms under the thermostat due to
incomplete filling of the cooling system or coolant loss, no coolant
will circulate between the engine and radiator, and the engine
will quickly overheat.
You can check for this condition by carefully touching the
upper radiator hose when the engine is first started and is warming
up. If the upper radiator hose does not become hot to the touch
within several minutes after starting the engine, it means the
thermostat is probably defective and needs to be replaced.
CAUTION: The replacement thermostat should always have the
same temperature rating as the original. Do not substitute a
colder or hotter thermostat on any vehicle that has computerized
engine controls as engine operating temperature affects the operation
of the fuel, ignition and emissions control systems.
DEFECTIVE FAN CLUTCH
On rear wheel drive vehicles with belt-driven cooling fan,
a "fan clutch" is often used to improve fuel economy.
The clutch is a viscous-coupling filled with silicone oil. The
clutch allows the fan to slip at high speed, which reduces the
parasitic horsepower drag on the engine. If the clutch slips
too much, however, the fan may not turn fast enough to keep the
engine cool.
The silicone fluid inside the clutch breaks down over time
and can leak out due to wear, too. If you see oily streaks radiating
outward on the clutch (and/or the fan can be spun by hand with
little or no resistance when the engine is off), it means the
clutch is bad and needs to be replaced. Any play or wobble in
the fan due to wear in the clutch also signals the need for a
new clutch.
EXTERNAL COOLANT LEAKS
Leaks in radiator or heater hoses, the water pump, radiator,
heater core or engine freeze plugs can allow coolant to escape.
No engine can tolerate the loss of coolant for very long, so
it usually overheats as soon as a leak develops.
A visual inspection of the cooling system and engine will
usually reveal where the coolant is going.
Leaks in hoses can only be fixed by replacing the hose. Leaks
in the water pump also require replacing the pump. But leaks
in a radiator, heater hose or freeze plug may sometimes respond
to a sealer added to the cooling system.
WEAK OR LEAKY RADIATOR CAP
If no leaks are apparent, the radiator cap should be pressure
tested to make sure it is holding the specified pressure. If
the spring inside the cap is weak (or the cap is the wrong one
for the application), the engine will lose coolant out the overflow
tube every time it gets hot.
INTERNAL COOLANT LEAK
If there are no visible coolant leaks, but the engine is using
coolant, there may be a crack in the cylinder head or block, or
a leaky head gasket that is allowing coolant to escape into the
combustion chamber or crankcase.
EXHAUST RESTRICTION
In some instances a severe exhaust restriction can produce
enough backpressure to cause an engine to overheat. The most
likely cause of the blockage would be a plugged catalytic converter
or a crushed or damaged pipe. Checking intake vacuum and/or exhaust
backpressure can diagnose this kind of problem.
BAD WATER PUMP
In a high mileage engine, the impeller that pumps the coolant
through the engine inside the water pump may be so badly corroded
that the blades are loose or eaten away. If such is the case,
the pump must be replaced.
Most pump failures, however, occur at the pump shaft bearing
and seal. After tens of thousands of miles of operation, the
bearing and seal wear out. Coolant starts to leak out past the
shaft seal, which may cause the engine to overheat due to the
loss of coolant. A sealer additive will not stop this kind of
leak. Replacing the water pump is the only cure.
CAUTION: A leaky water pump should be replaced without delay,
not only to reduce the risk of engine overheating but to prevent
catastrophic pump failure. If the shaft breaks on a rear-wheel
drive vehicle, the fan may go forward and chew into the radiator
ruining the radiator.
INOPERATIVE FAN MOTOR
On most front-wheel drive cars, the fan that
cools the radiator
is driven by an electric motor. A temperature switch or coolant
sensor on the engine cycles the fan on and off as additional cooling
is needed. If the temperature switch or coolant sensor (or the relay
that routes power to the fan motor is bad), the fan won't come on when
it is needed and the engine will overheat. Likewise,
if the fan motor itself is bad, the fan won't work.
The system needs to be diagnosed to determine where the problem
is so the correct component can be replaced.
Also check if you are not having a blockage in the coolants hose.
Take care and good luck
