Cooling system problems caused by a thermostat was the subject of a recent febi ProTip. The thermostat faults discussed were in some Chevrolet and Opel/Vauxhall models.

Problem
The engine cooling fan is constantly running, poor heater performance or the engine is overheating.

The engine warning lamp is illuminated - related to the symptoms listed above. These possible fault codes may be stored in the engine ECU:

• P0597 - Thermostat heater control system - open circuit.
• P0598 - Thermostat heater control system - circuit low.
• P0599 - Thermostat heater control system - circuit high.

Cause
An old, or incorrect, type of coolant is being used - causing corrosion or sludge build-up in the cooling system, preventing the thermostat to fully close or open. If the coolant temperature is detected to be above or below the optimum temperature range, the engine control unit has a built-in failsafe mode that will switch on the cooling fan.

Solution
Before replacing the thermostat, inspect the electrical connection and check the water temperature sensor is operating correctly. Once the thermostat has been identified as the source of the issue, flush out the coolant system and replace the thermostat. Replace the manufacturer’s recommended coolant, bleed the cooling system of any air and clear the fault codes using a suitable diagnostic tool.

This ProTip refers to Chevrolet and Opel/Vauxhall models with LDC, LDD, LWD, A12XEL, A12XER, B12XEL, Z12XEP, A14XEL, A14XER, B14XEJ, B14XEL, B14XER, Z14XEP engines.