I Changed my themostate on my car about 2 month ago, now, yesterday, my car 's temperature gauge started jumping up to "H" again. what could be the problem now?

did I not install the themostate right? but it worked for 2 month....

what else could be the problem

 

Low coolant level, air in the system, water pump (unlikely), coolant leak, bad radiator cap. You can't really install the thermostat the wrong way because it comes with a housing, so there is only one way to install it. Maybe take it out and see if it's jammed or something. Also the worst that could of happened, you got a messed up headgasket, or cracked head (which is unlikely). Check you oil and see if it looks normal it might be watery.

Did you fill up the coolant after you installed the thermostat?

 

yea i fill up with half water and half coolant after i installed thermostat.

bad radiator cap? huh
coolant leak? I looked under the car.. i dont see anything leaking...


could it be bad radiator? how do i know if it needs to be replaced?

 

Is your coolant low now? Open the radiator and look if you can fill it up
And I don't recomend driving like that unless you wonna end up with crooked or cracked head.

 

One of my buddies at work stated at thermostats sometimes come off the shelf broken. You should maybe try replacing it again since it's only a 15 buck part. Good luck.

 

I agree with Bosa...IT may apply even more to the aftermarket part. Not sure if you still have the sales slip or any kind of purchase record, to get a new one. Even if is an aftermarket part, it shouldn t bite the dust after 2 mos. Try to see if you could get another one...