The first mechanic could never figure it out. I took the summary to the dealership, he read it and said 4 to 5 hours of troubleshooting at $129 per hour. I asked if after 5 hours of troubleshooting if he could guarantee an answer, he said no. I left .. quickly! Took it to another mechanic whom read the summary in front of me and immediately said he thought it was the heater core. He charged $150 to diagnose and ultimately bypass the heater core. Runs great!! Does not get over 190°

Apparently the original owner used stop leak in the engine which clogged the heater core.

 

Post #55.

 

A lot of people learned an awful lot if they followed this post all the way to the end, guppy. Heater cores are rarely on the troubleshooting radar unless they are leaking.

 

Roger that.. I never would have thought of that one.

 

I am not sure I can figure out how that would cause the problem. If it did it did, I just can't think the logic through.
I would appreciate an explanation for my future reference.

 

Well the water return from the head HAS to go thru the heater core and then return to the big hose. The little square port on back of the thermostat housing is where the water has to return from the head. The heater was getting hot, so it was not a complete blockage. However the lower radiator hose was not hot. I too have never came across this configuration. Back in the day, I would cap off (not bypass) the heater outlet so we did not get the heat inside of my pickup truck.

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The reason it is different is in the old days there was a valve controlling The water flow, now the heat is controlled by air flow.

 

I've read this whole thread and am now having sort of the same problem. My hhr is getting in the 230 degree range when it's idling and when you rev it up starts cooling back down. And when your going down the road it stays between 190 and 200 deg . I've changed the t stat and flushed and replaced the coolant with dexcool. This morning I let it run a little longer to see if the fan ever kicked on it got to 244 at idle with the a/c on and the fan never kicked on . I shut it down out of fear of causing damage!! I replaced the 30 amp fuse and the relay but fan still does not come on !! Any ideas on what I should I check next??
After reading this thread should I pull this thermostat housing and check this piece?? Is this piece hard to take off?? Did this fix your problem so far?? I know this still don't answer my question about that fan not coming but I'm thinking I might try this!! Any help??

 

A. The fan should come on when the a/c is on
B. The fan should come on at around 219F

So you need to jump the fan wires to see if it's broken. Sounds like the fan or its triggering is the problem.

 

It would be handy to include your other symptoms like the compressor making noise.

That means the a/c needs attention and yes, that could cause overheating.

You need a mechanic!