1997 K2500 454 Temp creeps up at idle

[MyTOY]

How can you tell and get the air out of the system? Thanks

[clampjockey]

i started my truck cold, waited for the thermostat to open. once it did, i shut the truck off, opened the rad cap to the first notch (be carefull, its hot) i used good gloves so you can keep good pressure on the cap with your hand, let the pressurized antifreeze shoot from your rad through to your overflow jug. once you let the pressure off, take the rad cap completely off, start the truck, refill the rad, while its idling it'll keep sucking more and more water lowering the level in the rad. keep topping it off till it stays full (might take 10 mins) then cap it and take the truck for a drive and see if it makes a difference. i probably shouldn't have posted this, because it could be completely wrong, i'm not a mechanic and i'm not trying to pretend to be one so i don't want to get bashed if i'm wrong. i had the same problem with my truck and it worked for me, heat guage never reaches half and my heater is so hot it'll chase you out of the truck. i didn't even realize that coolant systems sometimes get airlocked, until it happened to me in a z24 i had after an engine change. that particular model had a nipple on the thermostat housing for bleeding air out.

[CBRF Engineer]

Originally Posted by clampjockey

i probably shouldn't have posted this, because it could be completely wrong, i'm not a mechanic and i'm not trying to pretend to be one so i don't want to get bashed if i'm wrong. i had the same problem with my truck and it worked for me, heat guage never reaches half and my heater is so hot it'll chase you out of the truck.

Thanks Clampjockey, I'll try that.

[CBRF Engineer]

I went through my GM service manuals for my truck and it says that overheating at idle may be cause by a worn or bad PVC valve, TVV (Thermal Vacuum Valve), or ECT (Engine Coolant Temperature) sensor.

Does anyone know where the TVV is and what is it's purpose?

I just spent 2 hours going through the service manual and can only find two references to the TVV, one in the overheating section and one in the abbreviation section. I can't find it in the component location section at all.

[J-Ri]

The TVV (name may be different on mine... don't remember for sure) on my truck ('86 350ci) is on the left side exhaust. It's got a weight and a spring on it with a metal vacuum line attached. As a bi-metalic strip inside heats up, the vacuum changes.

[CBRF Engineer]

For anyone following this thread, here is where I am. I put an AutoXray scanner on the truck and the engine temperature at the thermostat runs between 199 F and 204 F. At idle and extended cruise it runs at 203 F to 204 F. When the throttle is constantly changing as in city traffic, it runs at 199 F. The gauge sensor is in the center of the drivers side head and does not seem to correlate to the temperature that the computer sees. From the GM manuals I have, the gauge reads higher the lower the resistance from the sensor. It may be that the sensor is starting to fail. I’m going to keep an eye on it and if the sensor is not too expensive, I may try replacing it this summer. Thanks for the help of everyone that posted.

Update:
I pulled the heads and had them surfaced and recut the valves. Everything is back together and the heating up problem is gone. I may have caught a head gasket failing at the early stages because there was no visible evidence of a blown head gasket.