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Temp gauge stopped working. I replaced sensor temp went to 100 then back to 0. Will changing thermostat fix this issue? Engine light does not come on!?
 

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08 convertible
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Watch the gauge carefully. Note the temp with the engine cold. Then run/drive the car and watch the gauge. Does it move up a bit to where it shows a low temp, like 100, or does it stay where it was cold? If it moves up a bit, chances are the thermostat is stuck open and the gauge is working fine. You can test further by running the car with something taped over the grille to block airflow to the radiator. Like you see truckers do in winter. Does the temp move up? If it does, it confirms an open thermostat.

If the gauge needle never moves from dead cold, or it moves suddenly and/or intermittently, it's an electrical problem in the sensor or gauge wiring.
 

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I replaced thermostat and all fine now. Never ran into this type of problem before! Lol no codes, not overheating, was a learning experience!
 

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08 convertible
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Lol no codes, not overheating, was a learning experience!
A thermostat stuck open does not cause overheating, which is the reason thermostats are designed to fail open. No codes because it's not a condition likely to cause damage or leave you stranded. The temp gauge is your hint that something is awry :wink2:
 

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Have you checked for pending faults? Check too if the fans are running at full speed when the gauge is out. Could be a P0128 pending fault. The P0128 is when the OBD thinks it takes too long to get up to temp. I have a bluetooth OBDII reader and can monitor coolant temp in real time. The thermostat seems to open and close fine and the sensor is obviously working too. I've been babying my '09 G6 convertible over the winter by holding off using the heater until the coolant temp gets over 160F and I don't get the problem. If my wife is in the car and turns on the heat before that, it usually trips the pending code. I can reset it through the OBD reader app in my phone and all is back to normal again. I've owned the car since it was new, this is the first year I've had this issue.
 
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