Oldblue

Like Don, I use the 50/50 already mixed Dexcool.
No guessing , no mixing, no debate about tap or distilled water.

guppy

Below is the thermostat out of the old engine with a blown head gasket.

guppy

Below is the brand new ACDELCO (ACD#131-158, GM# 12622410) thermostat.

donbrew

I can't make out the markings. Are the 180F? If they are the engine temp should hang around 190F while cruising.

Oldblue

The old one has a hole drilled in it? Old school but not great for a computer controlled Ecotec

guppy

The markings make absolutely no sense to me. I was hoping someone could shed some light on this. The new one is a 180F.

donbrew

Usually the diameter in mm and the temp in C. Any other marking are only meaningful to the factory.

I would expect an engine with a 190F to run just over 200F. And the fan to run most of the time, it is set to come on at about 219F and turn of at 180F.

guppy

UPDATE: The 2.4L engine was replaced with a 33K mile 2.4L engine from a junkyard. The person that owned the HHR before me said it has a brand new radiator. I replaced the thermostat with a new (ACDelco #131-158, GM# 12622410) and the lower radiator Hose (also ACDELCO). I fill it till it spills out with my mix of 50/50 green antifreeze and distilled water. I take it for a spin and park it in the driveway. When the temp hit 217°, the fan turned on, the temp dropped a little then began to raise, it got up to 225° and I got scared and turned off the engine. After it cools I will check the antifreeze level again. The A/C was turned off and the outside temp today is 68°. What's your thoughts.

Oldblue

Green coolant?

guppy

Super Tech Antifreeze - Walmart.com