Thermostat and Coolant Flow Diagnosis

Fix Soon

A hub for thermostat behavior, housing leaks, stuck-open running cold, and stuck-closed overheating.

Get this checked soon — it will get worse over time.

Check These First

Before diving into diagnosis, quickly verify these:

1Identify when the symptom happens
2Check warning lights and fluid levels
3Look for leaks, smoke, steam, or burning smells
4Do not continue if safety or overheating warnings are present

What exactly is it doing?

Pick the description that fits best.

Thermostat Housing Leak

Fix Soon

Thermostat Housing Leak points to a cooling-system temperature-control problem. Coolant level, thermostat behavior, fan operation, pressure control, and water pump flow should be checked before parts are replaced.

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Thermostat Issues

Monitor

Thermostat Issues points to a cooling-system temperature-control problem. Coolant level, thermostat behavior, fan operation, pressure control, and water pump flow should be checked before parts are replaced.

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Thermostat Stuck Closed

Stop Driving

Thermostat Stuck Closed points to a cooling-system temperature-control problem. Coolant level, thermostat behavior, fan operation, pressure control, and water pump flow should be checked before parts are replaced.

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Thermostat Stuck Open

Monitor

Thermostat Stuck Open points to a cooling-system temperature-control problem. Coolant level, thermostat behavior, fan operation, pressure control, and water pump flow should be checked before parts are replaced.

See causes →