How can Prius owners diagnose a bad thermostat at home?

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How can Prius owners diagnose a bad thermostat at home?

A simple way to test a thermostat is by checking coolant flow in the radiator when the engine warms up. If there’s no flow o r excessive flow at startup, the thermostat may be stuck. Discussing DIY diagnostic methods can help owners identify the problem without a mechanic.

Sandeep asked on 13 Feb 2025 14:48:48 pm

1 Answer

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Car Mechanic Expert - on 13 Feb 2025 14:58:55 pm

To test if your thermostat is malfunctioning:

Warm Up the Engine: Start the Prius and allow it to warm up for a few minutes.
Check Coolant Flow: With the engine running, open the radiator cap when the engine is cool and check for coolant flow.
If there’s no coolant flow o r excessive flow immediately after startup, the thermostat may be stuck.
Feel the Radiator Hoses: The upper radiator hose should be cold at first but should warm up once the engine reaches operating temperature. If it stays cold, the thermostat may be stuck open.