2004 Envoy overheating

I have a 2004 Envoy 4X4. I am having a problem with the water temp gauge. After driving for awhile (approx 25 miles) the temp gauge begins climbing but only while the truck is idling. Once I begin to move and the rpm go up the temp comes back down to normal (about 210 degrees). It doesn't happen every time I drive the truck but you never know when it will go up. I have had it in the dealers at least 5 times and they still haven't found the problem. They have changed the instrument cluster and also changed some switch in the steering column that they say controls all the gauges. Any help would be appreciated.

Welcome to AF. How high does it go? Has anyone verified the actual temp on a scanner under these conditions.

the gauge reading goes up to 260 degrees and the needle will bury on the high side. i haven't checked the actual temp and i don't know if the service tech did.

Does the fan go to high speed, the rad cooling, fan does the engine lite come on saying reduced power,?

If that 260degF was real, the engine would go into limp mode, or you'd get other symptoms and warning lights. If a dealership already swapped out your IPC and ignition switch, I would think maybe the temp sending unit for the gauge or where ever the temp gauge gets it's signal from.

Joel

When the temp goes up all the way the check gauges light does comew on. As far as the fan going into high speed will have to check if temp goes up again. Let me add this. About 2 weeks ago I took the radiator cap off to check water level. When I did there was a lot of back pressure and once the pressure was released the temp stayed okay for about 4 days and then went up again. I took the cap off again 3 days ago and again there was a lot of back pressure. Since then temp has stayed steady (210 D). Could the problem be the system is clogged somewhere and needs to be flushed?

Does the return hose (bottom) to the radiator get warm? Almost sounds like a thermostat stuck closed. If that is good I would have it flushed. The plastic radiator caps on these are not meant to be removed much, if at all. After you trace down your prob I would replace that too. What codes, if any, does the pcm have stored?
Carp

the gauge reading goes up to 260 degrees and the needle will bury on the high side. i haven't checked the actual temp and i don't know if the service tech did.

The speedometers on these things might lie, but the temp gauge usually doesn't. Especially when it gets all the way up to 260. You may want to have a shop (or do it yourself if you're so inclined) perform an engine block test on your cooling system, just to make sure you haven't actually blown a head gasket. Make sure you're not trying to diagnose a problem with a gauge that's telling you the truth.

Thanks for the reply, but the age of this thread denotes it's basically dead.