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EZ way to check thermostat


Hirsch's Avatar
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08-10-03, 11:01 PM   #1  
EZ way to check thermostat

Take the thermostat out of the car and put it in a small pot or coffee can and cover with water. Heat to a boil. If it doesn't open, it is most likely bad. Hope this helps those who have questionable thermostats.

 
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08-11-03, 05:47 AM   #2  
Joe_F
That is correct.

Best bet---thermostat is cheap insurance. Change it when you do a cooling system service. Replace it with a good quality OEM part for best results.

Thermostats also effect emissions as well as cooling system function.

 
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08-12-03, 08:06 PM   #3  
Start with a COLD engine, preferably the car sat overnight. Remove the radiator cap and make sure the radiator is full, if not top it off and wait a few minutes because it will usually need to be topped off again. With the radiator cap still OFF, start the engine and let it run a good 7 –15 minutes. The radiator will spill over a little coolant until the thermostat opens, but will then stay at a constant level of 1 – 4 inches below the opening. If the thermostat doesn’t open and is stuck closed, the coolant will spill up out of the radiator sort of like Old Faithfull at regular intervals. And, if you shut down the engine and the coolant continues to spill up out of the radiator, then you have a closed stat in a hot engine.I did one just like this last week.
Be careful working around a running engine, especially with the cap off and coolant spilling out.

 
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08-12-03, 10:46 PM   #4  
or you could just watch the scan tool--if coolant temp goes over 195 and it's not circulating through the radiator yet---a good bet that the thermostat is stuck closed. if the radiator is circulating well below 195---a good bet the thermostat is stuck open or physically broken.

 
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08-13-03, 06:01 PM   #5  
Definitely agree on the scan tool use. This is for the home mechanics who don't have a scan tool, but have more time to learn about their cars operation.

 
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08-14-03, 03:45 AM   #6  
Joe_F
Also, it would not work on an older car which has no computer

But I agree, the scan tool works best for a computerized car.

Alternatively, a temperature probe would do as well. Excellent tool for many jobs.

 
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