How do I know if my Thermostat isn't working. I have a problem whitch is if I am driving at night the heater doesn't work very well.. It works better if I only use 3rd gear :-/ Is this the Thermostat? Thanks

they are cheap and easy to replace so you could install a new one. and yes your t-stat could be causing this problem. not an issue now but if it is indeed your tstat then it could eventually end up in the closed position instead of open (causing no heat) and this would overheat your motor. not worth the risk in my oppinion.

 

if you want to test it, pull it out (with the engine cold!). with the engine cold the t-stat should be closed, so all you have to do to test it is look at it. if it's open at all then it is not working properly as it should be closed at room temperature. the tstat remains closed until the engine warms to whatever temperature the t-stat is rated for, then the t-stat opens to cool the motor. if it's constantly open (or you don't have a tstat at all) then the coolant keeps flowing and the engine never really gets hot, neither does the coolant, neither does the heat and neither do you. so if you take it out and it's open, it's causing your no heat problem. you can also plop it in a pot of water on the stove and heat it up to see if it opens all the way up at it's rated temp. but if yours is stuck open then you don't need to do that.

 

if the t-stat appears fine then youll want to pull both heater core hoses and run a garden hose through one side to blow out any trash accumulated in the lines to/through the heater core.

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How much should the thermostat open while sitting in boiling water?

 

I presume more than about 1/8" of an inch? That's as far as my two new OEM subaru ones opened.

 

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don't know, never tested one. i replace them every so often and have never had one go bad.