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 pressure.

Missing fan shroud or fan operating outside of the shroud.

Improper air flow to the radiator. Some cars require spoilers to direct the air flow across the radiator for proper cooling.

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 reverse direction.

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 control.

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 late.

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