lw9090

It is an ACDelco 180 OEM

donbrew

Well, the one you have is stuck open or the temp sensor is defective. I can't think of any other reason it would run too cold. Maybe an air bubble fooling the sensor.

Topping out at 160F is pretty low, mine would run 172F when it was stuck.

lw9090

I just went out to lunch and the temperature started registering again and stayed between 180-193. How do I check and get rid of an air bubble?

Oldblue

Park the HHR with the front end higher than the rear, let the HHR cool off then remove the pressure cap and check the coolant level and top up if required.

Rzrman328

First post but been lurking around...

Same issue as original poster....first time, replaced tstat with a Napa tstat. Ran anywhere from 168-171 degrees. That worked for about a week until the ---f came back. Then today, I replaced my tstat with acdelco and my temp gauge/ ac is working again. It is now running anywhere from 183-189 degrees. My concern is that my CEL never came on at all, ever. Is that something else I should be concerned about or maybe it's just one of those electrical gremlins? Thx.

donbrew

Well there is a lot of info here about coolant temps. Here are some highlights:

A. Above 180F is "normal"
B. Below 180F is BAD
C. Assuming the code you got was P0128, the problem is the coolant did not warm up to 180F fast enough. The CEL does not always come on.
D. The t-stats job is to get the temp UP, not down.

Rzrman328

Ok I'm back again....

So I put a GM thermostat in the car...it ran good, no issues everything working fine for a couple weeks. Temps were fluctuating between 195-204 normally driving so I thought it was fixed.

Yesterday I get the "---" again. And no a/c.

Temp sensor? Ecu? Any suggestions thx.

donbrew

Usually that means too cool, or the ECU thinks it is.
Easiest thing is to pop the T-stat out and inspect it, next would be the sending unit. ECUs don't normally break.

Rzrman328

Before I pull the tstat out (again) you think it would be bad? I just got it brand new.

The ac delco did work better than the Napa tstat as the Napa tstat never registered temp over like 180.

donbrew

Could be defective or they gave you the old design or some other piece of junk floating around the coolant. You have to take it out to get to the sensor anyway.