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Discussion Starter #1
The weather around here has been in the 30s for a little while now. The other night it was 16 degrees outside and as I was driving home, my check engine light came on. When I scanned it, it said that coolant temp was too low. I noticed that my coolant temp would stay around 160-170 when it's really cold ( 25 or less) and it's usually between 180-190 as long as it's over about 30 degrees outside. Is the change in coolant temp normal for really cold weather? I'm guessing the light came on because the engine computer is not used to seeing outside temps below 20 or 25. What temp does your 2.2 Cobalt run in really cold weather?
 

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Thermostat is design to keep engine at constant temperature no matter what the temperature is outside. So my guess is you need a new thermostat.
 

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Either thermo or you have the wrong coolant in. I'm in MN so mine sees bellow 0 from time to time and still runs at 190
 

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Discussion Starter #4
I'm running 50/50 Dexcool and water so I'm not worried about that. Guess I'll drive a while longer and see what happens.
 

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I'm running 50/50 Dexcool and water so I'm not worried about that. Guess I'll drive a while longer and see what happens.
it clearly states NOT to mix water with the dex-cool. Factory coolant is 100% dex-cool, states on the bottle "DO NOT ADD WATER". I believe it also says "gm certified" on the front (mine did)

I'm running the same coolant in my engine as in my heat-exchanger/intercooler setup and our temperatures reach well below zero (often below -30 degrees celcius) and no problems with it being too cold.

Also, as others mentioned your thermostat could also not be working right.
 

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Probably want to swap the coolant and the thermo now.
 

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Discussion Starter #8
I didn't buy premixed coolant. I used Zerex brand Dexcool. I plan to replace the thermostat this week. I'll try to get back in here and let y'all know if it's fixed.
 

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^Correct. No water, just like you NEED to use straight synthetic oil with these cars. Sounds crazy but thats what you get when Opel is building your engine!
 

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FLush the system and get the water out of it... you're going to ruin your car.

Straight DEXCOOL ONLY... read your owners manual.
yes exactly. use proper dexcool only, which came originally with the car. It only costs like $15-20 for a big thing and it will last you a long time...

^Correct. No water, just like you NEED to use straight synthetic oil with these cars. Sounds crazy but thats what you get when Opel is building your engine!
you don't need to run synthetic in these engines. Most people don't. I run Mobil 1 full synthetic for several reasons, one being my turbo upgrade.
 

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Discussion Starter #12
I'm not repeating this again. I DID NOT use premixed coolant. I mixed it 50/50 with water as recommended by the coolant manufacturer and by the 05 Cobalt owner's manual page 5-23 and 5-24.

Anyhow, the thermostat was the problem. The inner gasket was boogered petty good and it keeps constant temps now with the new one installed. I just recommend that if you're installing a header or if you have the exhaust manifold off for any reason, go on and install a thermostat. That makes it a lot easier, even for a 5 speed.
 

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I'm not repeating this again. I DID NOT use premixed coolant. I mixed it 50/50 with water as recommended by the coolant manufacturer and by the 05 Cobalt owner's manual page 5-23 and 5-24.

Anyhow, the thermostat was the problem. The inner gasket was boogered petty good and it keeps constant temps now with the new one installed. I just recommend that if you're installing a header or if you have the exhaust manifold off for any reason, go on and install a thermostat. That makes it a lot easier, even for a 5 speed.
okay, if your car was an 05 and it specified to use a 50/50 mix then that's fine, the newer cobalts (including mine) specify the GM certified dex-cool with no water, that's why we were concerned.

Glad you found the issue and got it fixed! and my original exhaust manifold was a bit of a pain to get off, the turbo manifold was even worse to get on :p
 

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Glad you found the issue. I was going to say that if you have an aftermarket intake then that could be the issue. My balt is used to FL weather and coming to OH i noticed that during really cold weather my check engine comes on but no code will be associated with it
 
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