I changed my thermostat with no problems until I went to put the housing on. One of the two bolts holes that tightens it down stripped. How do I fix it?

 

A re-read shows you mean the housing it attaches to (You say the bolt is stripped - then you need a new bolt.) But I expect you actually mean that the housing that the bolt screws into is stripped? If that is the case, then it needs to be drilled out and retapped for a slightly bigger bolt.

Mentioning what engine you have would really help. 2.2/2.4 or 2.0 turbo?

edit: after looking at some documentation it looks like the lower housing for the thermostat is a bolt on item, and is separate from the block. A replacement will be available from GM.

 

replacements for that lower housing:
(Without knowing what engine you have, nor what year )
https://www.ebay.com/p/2-4-Chevy-eco...Pipe/657164745

It's listed here as item number 8: (but no listing for it)
https://www.gmpartsnow.com/oem-parts...bC1sNC1nYXM%3D
Note at the bottom it states they don't carry every single part so contact your local dealer.

 

Junk yards have lots of them. They "should" be cheap as they are made out of really cheap soft metal; almost pot metal.

 

Welcome to the site, You could reach out to hellshotrod, he’s parting out HHR’s

 

Sorry. I never thought to add the other information about motor size. I have a 2007 HHR LT with a 2.4 motor. I didn't know the bottom housing could be bought. I ended up drilling out the stripped bolt hole and running a longer bolt and nut through the housing.

 

Good fix - and a whole lot cheaper than the housing replacement. Just keep an eye out for leaks for a few days and you should be just fine with it.