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2002 chevy trailblazer_lt_ext
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365 Posts
Discussion Starter · #1 ·
First off, this doesn't present like a bad thermostat. Also, I have no DTC's present.

On my way back from Ft. Wayne, I pulled in to a gas station to fill up. I had been traveling on the freeway for almost an hour at 75 mph, so then engine was warmed up. After filling up, I got in the TB and started her up. (engine was stopped a total of 10 minutes) The temp gauge was reading full cold. The engine was also idling like it was cold- 1200 RPM. I stop the engine and re-start- same thing. I wait for the RPMs to get below 1000 and pull away from the gas station. While sitting at the light to get on the freeway, the gauge suddenly jumps from below 100 F to 210 F. I thought this was a fluke, but it has done this 4 times in the last week. I don't think it is a stepper motor in the cluster, because the engine idles like it is cold when this occurs.

Any ideas? Anyone ever experienced this?

Thanks in advance! :weird:
 

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2004 gmc
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26,181 Posts
Could be a bad sensor or wiring, but wiring problems should throw a code. Confirm it if you can with a Scangauge or something that can read the data stream coming out of the sensor. You can feel the radiator hoses to make sure there is hot coolant flow, or turn on the heater.

The ECT sensor is located right above the thermostat housing & hose connection on the driver's side.
 

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2002 chevy trailblazer_lt_ext
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365 Posts
Discussion Starter · #3 ·
Thanks, Roadie.

There was plenty of heat out of the HVAC- it's been kinda cold in Indiana, lately. I didn't check the hoses, but every time I fuel up, I check the oil, tranny, power steering, coolant, belt, etc. under the hood- don't remember seeing anything out of the ordinary. I'll try the scangauge next time it happens. I'm leaning towards a bad sensor because the cooling system on this truck has not been touched since the dealer flushed it two years ago and the coolant reservior is full- this would lead me away from suspecting an air pocket. Also, up until now, the temp has always been right at 210. :undecided
 

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2003 chevy trailblazer_ls
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1,708 Posts
It is possible you have a vacuum leak in the small hose from the rad. and the reservoir. The rad is trying to refill but the leak is not letting it refill. Check the rad and see if it is really full.
 

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2003 gmc envoy_slt
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7,190 Posts
:iagree: with the sensor, but I would remove the radiator cap to check. When you had the radiator serviced, was the cap replaced? If not, you may need a new one.:m2:
 
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