Question about 1990 GMC Sierra

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My 1990 gmc sierra 1500 temp. guage stuck after new thermostat.

I have replaced the thermostat and check insure that the coolant level and mixture is acurate. I replaced the thermostat in hopes that the temp. guage would read accurately but it is stuck in the highest position. The vehicle isn't over heating but I would really like to fix this for peace of mind. Any advice or solution would be greatly appreciated. Thankyou.

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Does your temp guage needle drop to Zero when you switch off ignition ?

If not, your temperature transmitter is faulty, or the wire running to it is earthing out somewhere.

Hope this is of help.

Good Luck !


Posted on Jan 16, 2009


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Hi there,

Firstly - DO NOT run engine, when guage reads hot, as this will cause costly damage to head gasket & alloy engine head.

The fact that guage takes 1min to read HOT, would confirm the guage IS working properly.

So, other components which are likely to cause hot readings (in this order) are:

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If you still believe all of the above components are OK, then have your cooling system "pressure tested". This test should be done, before looking further at other electrical components.


"if this has helped you in any way, please rate this solution"

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Sounds like there may be an air pocket in the system.
Try 'burping' the system. If this still doesn't fix the problem, check the temperature of the heater core hoses (in and out) The inlet should be fairly cool, the other should be piping hot. If they're both cold; the heater core has an internal blockage.

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Bleed the system accordingly, and keep me posted!

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