If your thermostat runs at 190 degrees, it isn’t an AC Delco 131-158 180 degree thermostat.

 

Do you meant the temp while running stays around 190F or the t-stat opens at 190F? Running at 190F is normal, running at 180F is not.
The tstat should open at 180F then the cooling fan turns on at about 219F and stays on until the tstat closes at about 179F. Unless the AC compressor is running, then the fan is always on.
The tstat's job is to keep the temp ABOVE 180F the fan/radiator's job is to keep the temp BELOW 220F.

 

Mine runs steady at 183 degrees F

 

Mine runs at 182 degrees F. With AC Delco 131-158 thermostat.

 

It's the same one, cost me $55, wrong ones are a lot less. And the A/C still works.

It's running at 190° and that's with the A/C and fan always on.
The temp here since I put it in has been a heat index of 105 to 110° every day for the last couple months.
Overnite it has been dropping to 84° and it will then run at 185°
Keep in mind the A/C condenser is causing very hot air to flow thru the radiator adding to the load.

 

The important message is the coolant temp is "normally" between 180F and 200F while at highway speeds; occasionally up to 219F is OK if sitting still.
Overheating is consistently above 220F. Underheating is below 180F.

 

If it runs at 190 F plausible that there’s air in the cooling system, do a couple of burps.

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

 

Mine always stayed at 189F. 189F is nothing to put angst into.

 

Which one did you get? Is it the 1 1/4" hose model?

Since I'm replacing the engine in my daughter's HHR, I might as well replace the filler neck and hoses.

Steve

 

1 1/4 inch o d one .