The thermostat regulates coolant flow to keep the engine in its optimal temperature range.
A wax pellet expands at a calibrated temperature, opening a valve to let coolant flow to the radiator. Below that temp it stays closed for fast warm-up.
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Replacement runs $150–$500 including parts and 0.5-2.5 hours labor. Exact cost depends on vehicle, parts tier (OEM vs aftermarket), and local labor rate.
Expected lifespan is 80,000-120,000 miles. Driving conditions, climate, and maintenance affect real-world life.
Overheating (stuck closed); Engine never warms (stuck open); No heat from vents; Erratic temp gauge; Check-engine light P0128.
Most modern thermostats are sealed units that get replaced rather than rebuilt. A shop will diagnose, confirm with a load or output test, then swap the unit and verify operation.
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