Engine Cooling — Pinpoint Tests — Pinpoint Test B : Pinpoint Test

The Engine Overheats

Normal operation and Fault Conditions

The engine cooling system maintains the engine temperature during operation. Correct coolant flow through the engine, radiator and remainder of cooling system passages and components is essential to maintaining a correct engine temperature.

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. Coolant is sent from the coolant pump through the engine block and cylinder head. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump circulates the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant flows through the radiator circuit to transfer engine-generated heat to the outside air.

Engine overheating generally occurs when there is a disruption in the ability to control either coolant flow at the correct rate, the inability to transfer heat from the engine through the coolant (including low coolant) or an inability to transfer engine-generated heat to the outside air through the radiator.

Possible Sources

Low coolant level

External engine coolant leak

Airlock in system

Pressure relief cap installation

Restricted airflow through A/C condenser/radiator

Internal engine coolant leak

Coolant condition/concentration

Non-OEM engine enhancement components

Electric cooling fan

CHT sensor

Radiator

Thermostat

Coolant pump

Coolant flow restriction

Diagnostic Trouble Code (DTC) Fault Trigger Conditions