How to Diagnose a Failed Car Thermostat: Two Easy Symptoms

by Marjorie, Cars for Keeps Social Media Manager

Your car's thermostat would easily fit in the palm of your hand, yet like many vehicle components, a properly functioning thermostat is critical for engine health and proper vehicle function. It regulates your car's engine temperature, a critical factor for engine health.

Some of you may be inclined to cut repair costs by performing a "simple" thermostat replacement yourself. eHow details how to replace your car's thermostat in 11 not-so-easy steps. I'm sure these instructions look very simple indeed to an auto mechanic, but for the rest of us, it looks like a path down the road to almost certain failure. Unless you're a mechanic yourself, cutting corners by replacing a thermostat on your own will likely end in far greater costs - like an improperly installed thermostat and an overheated engine. Watch the Cars for Keeps Coupon page, Frequently Cars for Keeps offers free thermostats for thermostat replacement jobs - a far cheaper (and easier) option than attempting to do the job yourself.

Diagnosing a failed thermostat, however, isn't difficult at all.


How to diagnose a bad car thermostat:
Most car thermostats fail in one of two ways: they become stuck either in an open position or a closed position. A closed thermostat valve will cause the engine to overheat, harming the engine and potentially destroying the head gasket, while an open thermostat valve will over cool the engine, causing it to work much harder than necessary.

The symptoms for both an open and closed stuck thermostat valve are relatively easy to tell. A closed thermostat valve (overheated engine) will be indicated by your vehicle's temperature gauge plunging into the red. This may happen slowly or quickly, and wintertime driving may make this symptom less severe, but a vehicle that's running hot should always be brought to a mechanic immediately. An open thermostat valve (underheated engine) is indicated by a car not putting out as much heat through the vents as it should, and by automatic transmission vehicles having difficulty shifting to higher gears. The latter may be more difficult to tell in summertime, when heating vents aren't used, which is another good reason to always be attentive to your vehicle's engine and transmission performance.

If any of these symptoms describe your vehicle, bring it in to Cars for Keeps immediately for a quick test, and have a cup of coffee while you wait.

Safe driving!