I have a 1997 K2500 with a 454 that was actually built on the 1998 assembly line. I was a GM employee when I ordered it. I flushed the cooling system a couple years back but it has now started to show the temperature creeping up at idle. It actually gets up to the 3/4 mark but when you bring the rpms up to 1000 or over, it goes back down just below the 1/2 mark (210 deg). I've tried different thermostats with no change. So far it has not lost any antifreeze. Any help would be appreciated. Thanks.

clutch fan?

try draining and measuring the amount of antifreeze thats in your engine.you may have part of your radiator blocked.happened to me on a 89 k2500.the only way to avoid this is to flush radiator every 1 to 2 years.

sounds like a bad fan clutch

What does the temp guage read (As far as degrees)?

Time to ditch that mechanical fan and slap on an electric fan.

Look under the hood and see if the fan is turning at idle. Actually alot of these new engines will creep up pretty hot 3/4 mark or sometimes slightly above. I dont know why but ive seen some that do. If it is an actual problem id see what your radiator looks like. Sounds like at idle your airflow across your radiator isnt as good as it should be.

First, thank you to all that replied.

The fan clutch is tight and seems to be working. This is a heavy 3/4 that I special ordered with 1 ton axles and front springs. Actually the only difference is the 1 ton ext cab has duals and one more rear leaf spring. This truck has both electric and clutched fans. There is radiator stacked on radiator on this thing. It uses the power steering pump to drive the power brakes so there is also a power steering fluid cooler/radiator from factory. I drained the fluid down (easier said than done) and the radiator was clean all the way to the bottom. It was below zero here and I let it heat up at idle. The radiator stayed cool but the temp gage showed 3/4 and not the normal 1/2 (210F) when the rpms are up. It seem like the pump just doesn't push enough water. I don't know if this is normal becaue I just the temperature was that high after sitting in the truck waiting for my wife. It was below zero and I wanted to stay warm.

BTW, one day I did smell and notice some anti-freeze towards the rear of the engine block on the ground one day but did not know if was from my truck or another vehicle. I have watched it ever since and I have not seen it since.

Thanks again.

As for the temperature at the 3/4 mark, the gage says 100 at the low end, 210 in the middle and 260 at the high end. So, your guess is as good as mine at the 3/4 mark. I'd guess about 240F, but that's just a guess.

I am about to change the intake gasket on my truck(k1500 w350) Does anyone know if the 454 has the same intake leak problem?

CBRF Engineer- Try getting a scan tool on your truck and see what it reads. Sometimes those gauges arent always on the money. If you also have electric fans id check your fan relay and make sure those electric fans are kicking on when they should be. If you just let it Idle some more after it creaps up to the 3/4 mark will it keep going to the red??? Or does it eventually kick the fan on and take it down to around where it should be? Put a piece of cardboard down under your truck at night. That'll show you if the leak is coming from your truck, and where abouts its coming from.

Riche- I dont really know if the 454 would have the same problem. I would assume so cause I heard the intake problem was related to the gasket itself. If they got all thier gaskets from the same manufacture and they were made out of the same materials I would assume they could have the same problems as the 350. Just what I think though.

take it to a mechanic and have them use one of those infared temperature sensors (whatever their called) and find out what the actual temperature is.

Factory guages are usually crap. The one in my Chevy reads about 250* when it is actually 180* (and I've replaced it with several others and their all off)

infared temperature sensors are not a very good way to tell engine temp. Get a scan tool with data read out hooked up and get a true reading

Thanks again to all that replied.

I took it on a trip to my inlaws cabin. Running around town, it runs at the 210 mark on the gage. Long highway cruises it runs half way between the 210 and 3/4 mark. At idle it runs at the 3/4 mark. We replaced the thermistat again and tried it pulling a heavy load up hill to see if it would heat up any more, it still ran half way between the 210 and 3/4 mark. The fan clutch seem to be working and when coasting to get air through the radiator but letting it idel, it still heats up to the 3/4 mark. So I don't think it is a fan issue. The truck is kept in a heated garage with a clean sealed floor so any leaks would be very noticeable. We are going to put a pressure test on the system for 24 to see if holds or leaks outs. I'm wondering if I have a blown head gasket but heavy loads does not make it heat up. My father inlaw has an AutoXray tool, and I'll see what that says the temp is doing. Any other ideas?

Sounds kinda normal to me. They usually heat up alittle more when standing still. I have a 96 Camaro and that gets up to the 3/4 mark at idle. But once it goes alittle past the fan kicks on and you can see the temp drop down to around 5/8 then start back up once the fan kicks off. Just make sure that cycle is happening when it idles and your truck should be fine. If you can let it idle for 20 minutes and it doesnt overheat I wouldnt be worried about it.

i think that's too hot. i get sketchy if mine reaches half. mine used to do that ( reach 3/4 or more). i'd checked the rad several times when cold, and it always LOOKED full. as it turned out, it was slightly air locked and low 3/4 of a gallon of antifreeze.

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

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.

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.

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.

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.

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.