Hi everybody,
I'm here to pick the brain of the brightest HHR gurus.
Subject: 2007 HHR 2.4 manual with 165K on the clock
Let me give you the back story as any detail can be useful.
About a month and a half ago I cleaned the throttle body. It was so dirty that I had to scrape off the buildup with my fingernails because the throttle body cleaner would not get it off. Of course I got the high idle problem afterwards. I drove the car like that for about 2 weeks hoping that the computer would figure it out but it did not. I ended up taking it to the dealer where the tech flashed the 2 programs available for the 2 different injectors and that finally fixed the high idle. Before this the cooling fan would turn on at 208F and cool the engine nicely. After the reflash I noticed that the engine would heat up past 215F so I figured that the thermostat failed. Replaced it with a fancy fail safe one that blows open when the engine overheats. After the first drive it blew open and now the engine temp settles around 165F when moving. On my way back from work I was sitting in traffic and noticed that the cooling fan would turn on at 217F but would not shut off even at 130F. I dug around this forum and found out that the 217F is normal for the fan to kick in but then it raises the question why the thermostat blew open. I swapped the relay to rule it out sticking but it made no difference. I tested it 3 times with same results. I will swap the thermostat back to the old one.

Any help is much appreciated!
Krisz

Solution: The thermostat was defective. If the coolant reaches 217F and the fan turns on it won't turn off until the car starts to move.
One more thing. When the engine heats up over 210F it starts to sound like a diesel tractor and has reduced power. Maybe the temp sensor is failing and reads too low? But that still doesn't explain why the cooling fan refuses to turn off...

 

ACDelco 131-158 thermostat. All others can cause problems.

Thermostats almost always fail open, causing the engine to run cold. If it was running hot, look elsewhere. A leak, or maybe a bad pump.

 

First get the correct t-stat. AC-Delco 131-158 180F ONLY.
Second the t-stat's job is to keep the temp above 180F NOT below.
Third have you ever changed the Dexcool? it has a shelf life of 5 years. Have you checked the copolant level under the pressure cap? Don't use other than 50/50 Dexcool.

Correct behavior is: get up to 180F in less than 5 minutes, while cruising should stay around 190F fan turns on at 217F OR when the AC compressor is running. The AC compressor runs when the mode is set to defrost or if the recirc is on, with no indicator light.

 

I will put the thermostat back in that I pulled out because I thought it was the problem. It is relatively new (less than 2 years) and it is an ACDelco. There is no leak, I also replaced all hoses. Water pump is about a year old with all seals in the back. System is full of coolant.
Cooling fan turns on at 217F which is normal it seems like but does not turn off once it's on unless I shut the car off. A/C was not on nor the defogger.

 

I'm swapping an ACDelco back in tomorrow but the problem existed with that as well. Car runs cold because current tstat is stuck open. The problem is that the cooling fan does not turn off when coolant is back at normal temp. It stays on until I turn the engine off.
Coolant was drained about a year ago when I replaced the water pump and again yesterday when I replaced all hoses and thermostat. I did not have any of these problems until the ecm (or whatever GM calls it) was reflashed.

 

Then take it back to the dealership that did the reflash.
2 different injectors? Did you fully burp the coolant?

 

ACDelco sells several part numbers. That's why I was so specific. It is the physical mechanical design that is different.
T-stats don't usually cause overheating, they open at 180F and stay open. It is the pump and radiator's job to keep the temp below 220F.
The usual point of failure is the inner rubber gasket deforms and sticks the valve open.

He's talking about that 2007 TSB about the wrong injectors/programming from the factory, hard to believe it took 15 years to manifest.

 

I read it somewhere (not sure if it was here) that the only way to fix the high idle after throttle body cleaning is to reset the computer. Chevy did not implement a way to reset it oddly enough and just simply reflashing the same software onto the computer does not fully reset it either. The 2.4l engine came with 2 different injectors. Grey and blue IIRC. Flashing back and forth between the 2 softwares can force the computer to fully reset. The tech at the dealership did exactly that without me telling him anything and told me the same story afterwards.
As far as I can tell the system is air free. When I swap the stat again later today I'll make sure it's fully bled and report back if it fixed the fan issue but it does sound like I will have to take it back for another reflash.
There is only 1 temp sensor on the engine, correct? So if it was affected by trapped air the temp on the cluster would read false. But that temp drops with the fan on well below 190F and the computer does not shut the fan off. Therefore it has to be the computer as I have ruled out a sticking relay. Am I correct or missing something?

 

Been reading this and watching.
If the car is getting up to 217 and turning the fan on, then it is getting too hot. You need to find out "why" it is overheating.
Also seem to recall an old thread about once the fan comes on for overheating that it won't turn off until the key/ignition is cycled off/on.

My guess is if you fix your running hot problem, then it will fix the fan issue.

 

I also feel like it's not suppose to get that hot and it didn't before the reflash. But others say it's normal. I did not get a CEL but after an hour of driving back from work when the new stat blew open already the temp reading on the cluster went away and displayed "---F". The needle also dropped to the bottom. I checked if there were any codes and there was one for failed tstat / low engine temp but nothing for overheating. I also don't like the fact that when the engine temp goes above 210F it starts to sound like a diesel engine and has slightly reduced power. I'm starting to think that I might have a blown head gasket. There is no milkshake going on but when I had the high idle issue I was watching on a OBD2 reader what the computer was doing and I saw some weird stuff going on. Instead of closing the throttle body the computer was messing with the ignition timing to keep the revs under control. It went as high as 30 deg at idle (about 2300RPM). I could force it to idle normally by putting it in gear, keeping my foot on the brakes and releasing the clutch until revs dropped under 1000RPM. After keeping it there for about 5 seconds the computer would figure out what to do, sort itself out and idle normally until a slight touch to the accelerator and it would run away again,