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Discussion Starter #1
Hello everyone. The other day my CEL came on and had the code P0128 which I am familiar with from about 2 or 3 years ago when I replaced my thermostat with an AC delco thermostat. When the light came on my coolant temperature wasn't reading above 180 F I don't believe. I'm sitting at idle right now after some driving and my coolant reads 189 F and the outside temperate is 36 F.

Does it sound like I need to replace my thermostat again?
 

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Discussion Starter #2
I forgot to mention that my coolant level in the expansion tank is above the cold fill line and I don't have any driveability issues. 2005 Cobalt 2.2L base automatic
 

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I'm sure you already know what that code is, but for anyone else looking at this thread later on, here's the English version:

P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
My guess is that replacing the thermostat would probably clear up the issue. I'm a little surprised that yours is going out so frequently since I've never replaced mine and it's been going strong for ~6 years. How many miles have you racked up?
 

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That code means your engine didn't reach operating temperature in the pre-set delay. This means your thermostat isn't closing tight or the rubber seal has failed.
 
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That code means your engine didn't reach operating temperature in the pre-set delay. This means your thermostat isn't closing tight or the rubber seal has failed.
The last time this happened I replaced it with an AC Delco stat. Should I look into a different one?
 

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What did you do???or get done.
 

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Discussion Starter #11
They replaced the thermostat and a gallon of coolant. According to them the previous person who replaced the thermostat put it in backwards. Very interesting.
 
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