Engine Overheating Problems After Rebuild
AERA members have reported overheating problems with various
engines after a complete rebuild. Most of the time the engine
will operate normally at low rpm, or "around the town driving".
Increasing engine rpm and load will cause the overheat condition.
When an overheating condition is evident check for:
Defective dash gauge or sending unit. Always double
check your findings with an external gauge or a
thermometer in the coolant.
Coolant mixture of antifreeze and water. A coolant
mixture of more than 70% antifreeze limits the
coolant's ability to transfer heat and can lead to
engine overheating. Not enough antifreeze lowers the
boiling point of the coolant.
Radiator pressure cap that maintains the rated
Missing fan shroud or fan operating outside of the
Improper air flow to the radiator. Some cars require
spoilers to direct the air flow across the radiator for
Inoperative fan clutch or fan with missing or bent fan
blades. The fan may also be mounted in reverse. This
may especially be the case in late model engines with
serpentine belts where the water pump may turn in a
Inoperative electric fan, defective fan relay or chafed
wiring. Electric fans are often interconnected with
the wiring for A/C, be sure the fan comes on both when
the A/C is operating as well as for regular temperature
Water pump turning in the wrong direction. Again, this
problem may be the case in late model engines with
serpentine belts inoperative thermostat or thermostat that opens to
Collapsed radiator hoses. At times an older hose can collapse internally while giving a good outside appearance.
Blocked or restricted radiator or cylinder block. Rust
and corrosion can reduce heat transfer.
Blocked or restricted cooling passages in the cylinder
block from casting flash, incorrect head gaskets or
incorrect installation of the head gaskets.
Restricted exhaust system or blocked catalytic
converter. abnormal combustion caused by incorrect ignition timing
or defective emission controls.
It is important to check all of the points stated above
as part of diagnosing an overheating condition. Many
times an overheating condition can be solved without
changing major engine components or accessories.
The AERA Technical Committee
July 1988 - SB 158