Thermostat Failure (All Models)

Engine runs cold (temperature gauge barely rises from the bottom), or overheats suddenly. Heater blows cold air despite the engine running. Fuel economy worsens because the engine never reaches operating temperature.

The thermostat is a wear item that sticks open (engine runs cold) or sticks closed (engine overheats). The Ecotec V6 is particularly prone to thermostat issues. On V6 models, the thermostat housing also contains a bleed screw that can corrode and leak.

1. 1 Replace the thermostat. Use a genuine GM or quality aftermarket unit (Tridon is the standard recommendation). Parts: $20-40. Labour: 1-2 hours. On the Ecotec, always replace the housing O-ring at the same time. After refilling coolant, bleed the system using the brass screw on top of the thermostat housing -
2. 2 open it with the engine running until coolant flows without air bubbles