I Am having an issue with my 08 HHR. At first out was a leaky lower radiator hose. Took me some months to get fixed.. Once fixed got the hose and thermostat replaced.(non GM thermostat) because my car was running 🔥. Now i can drive for about 15 minutes and it shoots up to the red! I popped the hood yesterday and the radiator cap was cold but the dash temp says it's running hot... The AC works but the heat doesn't. Could it be my thermostat, water hose, electrical temp sensor or what?...any suggestions?...

 

Wut cap now?

 

The issue lies in the thermostat used. The vehicles are very picky.
Showing HOT but with a cold radiator cap tells me therre is no water circulating through the radiator.

 

Yes, that thermostat will cause issues and codes, I recommend an AC Delco 131/158 180 degrees thermostat .

There is air in the cooling system, you have to burp your cooling system to get it out.
Then wait till the code P0128 pops up, it might be a month or two.

https://www.chevyhhr.net/forums/how-...-system-60614/

 

I vote a clogged or air locked heater. Maybe a bad water pump. Maybe damage from letting a leak go for months.

T'stats don't usually cause OVERheating.