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Envoy temp gauge fluctuates

My temp gauge fluctuates between half way up and sometimes goes as high as 225 degrees especially in summer. What should I do to correct it to stay in center or just before?

Check the level in the radiator, it may be low. What condition is the car in, how many miles, maintenance history, check engine light on etc? You could have a bad thermostat, low coolant, head gasket leak, etc.

2002, 115K miles, coolant fine. Sounds like a pressure hiss when I shut it off? Other than that it always runs the same and when its cooler out the gauge shows just over half way. thx.

I have one, so this may not be an easy option for you- but hook a computer up to it and go for a ride, and see what the temp actually is. My GMC Sierra temp gauge reads higher than the truck actually runs. the gauges aren’t exact science, and it can lead to some unnecessary repairs if nothing is actually wrong.

You can also take an infrared temp gun and see what the water temp reading is where the temp sender is.


Not sure what year rours is, but the stepper motors in the cluster cause many issues for many people. I had 3 guages go out, tach, oul pressure and speedometer, tach and oil pressure just died, but speedometer would say going 65 while gps and my knowledge knew we were gong 35. Got 7 stepper motors and new bulbs for $22,I replaced them and all was fine. Alternative was $300 for a new cluster and $200 for programming. Some internet sites will replace your stepper motors for %65 was the cheapest I saw. Early 90s era?

I don’t see anything wrong with the coolant temp.

Midway up the temp gauge is 210 degrees

And about 3/4’s up the gauge is 225 degrees.

The thermostat for your engine is rated at 190 degrees.

So the engine is going to operate at a temperature above the thermostat rating.

So in winter, the engine will run at about 210 degrees.

In summer, the engine will run at 225 degrees or higher.

Because the AC is on because it’s hot, and the condenser in front of the radiator is throwing heat into the radiator, the engine temp is going to run at 225 degrees or higher.


Concur w/Tester, I doubt anything’s wrong. 225 is within the range of normal coolant temperatures. No harm done of course to do a proper cooling system service. Drain all the old coolant out, re-fill, and bleed all the air bubbles out. Recommended every 2-3 years by the manufacturers for most cars as preventive maintenance. If the thermostat is over 5 years old, that would be a good time to install a new one too. Thermostats live in a very difficult and corrosive environment and eventually almost always fail. New thermostats failing right out of the box isn’t an unheard of thing here, so ask your shop to verify the new one is working before they install it, using the pan of water on a stove and thermometer method.

Of course, I think you may need a new radiator because of the age of the car. Look at the back of the radiator where the fins usually rot off, usually at the corners where it is hard to see. If you are seeing green or white coloration you probably need a new one.

Missing fins between the tubes and you really need a new radiator. If temps go up when climbing a long hill turn the heat up full and the fan to max. If that helps then you should inspect the radiator.

This engine has a fan clutch that is electronically controlled. In the interest of fuel economy the clutch is duty cycled at normal temperatures (210-225F), greater engagement of the fan clutch will occur with high cooling system temperature, transmission fluid temperature and A/C pressure.

I wouldn’t advise to start replacing parts based on suspicion if the vehicle is displaying normal temperatures.

Thanks a bunch George!

Thanks Barky. But my question was about temp fluctuation.

Thanks to all of you for your expertise!

I’ve owned 3 of these in the Trailblazer style. Basically the same platform hence TrailVoy nomenclature being used and a site named that way.

The temp guage rising under higher ambient temps is definitely indicating you have something not functioning correctly or as efficiently as intended. Make sure coolant is fresh and full. The clutch fans are a weak link on these. If it turns super easy at rest then that may be what’s starting to fail. Could also be radiator but start with the basics…

Does it get warmer when you are not moving? When does the gauge read the warmest? Does it drop when driving and then come up when you are idling? If so it could be the thermostat (stuck open) or the cooling fan not working. The motion of the car cools the radiator. If you see this while driving and you aren’t heavily loading the engine, I would start to worry about the water pump or the head gasket. You would want it to be the water pump in this case.

One thing you can do to eliminate the possibility of the head gasket is to open the radiator or reservoir cap with the ENGINE COLD ONLY!!! DO NOT DO THIS HOT AS IT IS DANGEROUS! So, after the vehicle has sat turned off overnight, go out and remove the cap. Start the engine and look inside the cap. You should see some fluid motion but not air bubbles. If you see bubbles that can be exhaust gasses entering the coolant through a breach in the gasket, cracked block, or head. I wouldn’t let it run more than a minute or so. Turn the engine off and reinstall the cap.

What do you see?

So can I assume if it runs between 210 & 225 I shouldn’t be concerned? I am not use to any vehicle rising past just before half way on the gauge and not long after I bought it I drove from Florida to Massachusetts and back and didn’t seem to have any issue with it even with the gauge problem. Do you think just giving it an engine flush would help in any way? I do appreciate your expertise Nevada!