2004 6.0L Newbie: Overheating only under load?

[RaysnCayne]

Hey all, first-time Sierra owner, and first-time poster.

 

I bought my heavily-used (276K) 2004 2500HD about 6 months back. It's been great until this evening. I changed out a leaking driver's side exhaust manifold gasket and took it for a test drive. I barely got 4 miles down the road and saw it was up to 230 degrees! It's been a very rock-solid 200 the whole time I've owned it. I pulled off the road, put it in Park, and within 50 seconds it came back down to 200. I revved it a bit and still dead-solid 200. I went down the road and barely another couple miles and it's back up to 230+. With a couple pull-offs, I managed to limp it back home. It got up to about 240 at one point and seemed like it'd just keep rising if I hadn't pulled over. But it seems like it'll happily idle at 200 until it runs out of gas.

 

The fan clutch seems fine (it didn't spin freely after I shut it off). The top radiator hose is hot, but the bottom's not. And the heater isn't blowing hot air. Does that all point to a stuck/broken thermostat? Or might I have a cooling system that needs a good flushing?

 

 

 

 

[Formulabruce]

1. It originally came with DEX Cool, that needs to be flushed

2. Change the water pump, its due, and the thermostat

3. Flush that heater core and clean the over flow/fill tank

[dewfpo]

With that many miles on it, if the cooling system hasn't been maintained, the radiator may need to be re-cored as well. But, one thing at a time and do the easiest, cheapest first. A good flush, then a new thermostat as Formulabruce suggested.

 

DEWFPO

[RaysnCayne]

I take it you guys feel the main culprit is probably a bad/stuck thermostat as well?

 

I'm just puzzled about the odd timing as this suddenly happened after my exhaust manifold gasket job. Like, maybe something (rag) fell into the down pipe and is clogging up the cat or something. There isn't anything in the pipe b/c I was careful to cover up the down pipe as I did the work. Just seems really odd this happened immediately after I did this project. I guess the heater not blowing hot air eliminates the exhaust angle. Well, I guess idling at normal temp does too.

 

I'll give the thermostat swap and heater core flush a try. (I noticed the heater core inlet is looking a bit gunky and is weeping a bit.)

[RaysnCayne]

I really lucked out on this one. I went to Advance and bought $300 worth of water pump, thermostat, antifreeze, radiator flush additive and a fan clutch. But figured I'd start with a quick heater core flush first. When I went to remove the inlet hose from the core, the plastic coupler snapped like a twig. A quick You Tube search revealed this is a common problem with these trucks and can cause overheating. (Mine was leaking so that should've been an obvious sign to me in hindsight.) So I replaced it with a new one and - wah lah! Fixed! Back to my rock-solid 200 degree operating temp.

 

For once in my automotive life, I did the cheap/quick repair first instead of spending a whole weekend throwing lots of money and parts at it! Yay!

 

If I was planning to keep the truck, I'd probably have done all the parts replacing, or at least give it a good flush and put green coolant in. But I want to get a 1500 Sierra and get out of this gas-guzzling/rough-riding 2500HD. It's just too much for a DD vehicle. So I'm just doing the bare minimum to make her run safe and sound and move on.

 

Thanks for the input y'all.

[Swimmer8366]

Ah how much would you want for it? Lol getting will never go to a half ton after owning my 2500hd I'm pushing about 14-16 city depending on how heavy I am on her. When I run octane boost and better fuel she gets better about 16-17

 

Sent from my Z981 using Tapatalk

[RaysnCayne]

14-16?!! I'd take that any day of the week for what I'm getting now. If I was getting 15-16, I'd seriously consider putting up with the crashy suspension and non-powered doors (it's the stripper Work Truck model) and driving her for another 25K 'til the wheels fell off. But my last tank just barely fetched 13.02 mpg. My early mpg checks were in the 15mpg range. So I feel like something's off. If I can find/fix it and it gets back to a solid 15+ mpg, I may keep her.