- Extended idle periods
- Faulty water temperature regulator
- Very light loads
- Air vent valve
- Cooling fan clutch
- Faulty Thermostatically Controlled Shutter
When the engine is running with no load, the heat from the engine is removed too quickly.
Faulty Water Temperature Regulator
Check the water temperature regulator for correct operation. A water temperature regulator that is stuck open will cause below normal coolant temperatures. Ensure that the water temperature regulator opens at the correct temperature. Check the water temperature gauge for correct operation. Install new parts, as required.
Very light loads can cause low coolant temperatures because there is less heat generation by the engine. A slight restriction of the air flow through the radiator will correct this problem.
Check the air vent valve which is located in the water temperature regulator. Ensure that the air vent valve is not stuck open.
If the cooling fan does not disengage properly, the coolant temperature may drop below normal levels. Check the temperature sensor for proper operation.
Faulty Thermostatically Controlled Shutter
Check the operation of the shutters. The shutters should be completely closed at the temperature below the fully open temperature of the water temperature regulator.