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How to Replace a Prizm Thermostat

by Lisa Wampler

The Geo Prizm has a small, economical engine that relies on maintaining the correct operating temperature to keep the engine running at top condition. If the thermostat goes bad, the engine could overheat and cause the aluminum heads to warp. This can cause thousands in repair costs. Replacing a thermostat is relatively cheap and only takes a few minutes.

Open the radiator filler cap located on the top of the radiator. A Prizm coolant system is pressurized, so opening the cap will prevent radiator fluid from spilling out of the thermostat cover when it is removed from the engine.

Locate the top radiator hose and trace it to the Prizm engine. The part that the hose connects to on the engine is the thermostat cover. Remove the band clamp that holds the hose to the thermostat cover with a screwdriver. Pull the hose off the thermostat cover and hold it up so any fluid left in the hose drains back into the radiator.

Remove the two bolts that hold the radiator cover onto the engine. The thermostat sits inside of that cover. Once the bolts are removed, lift the cover off the Prizm and pull out the thermostat gasket and thermostat. The gasket and old thermostat can be thrown away.

Place the new thermostat into the Prizm engine and put a new gasket in place. Place the thermostat cover back onto the engine and replace the bolts. Replace the radiator hose and tighten it down again with the existing band clamp. Place the filler cap on the radiator.


  • To avoid being burned by hot radiator fluid, the engine should be cool when you complete this job. If any radiator fluid spills out it should be wiped off the engine and the fluid should be replaced via the radiator filler cap.

Items you will need

About the Author

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  • radiator humor image by John Sfondilias from