I am on here for my fathers truck, Well his old one. He just bought a new 08 3500 single wheel and in a week we are selling his old 06 dually. Well when on the highway about 70mph its running a bit over 200. I went to pass a car and hit about 80-85 mph and the gauge shot up to the redline and check gauges light came on. He told me it had done that once before and so he changed the t-stat but i guess that wasnt the problem. I took it to firestone yesterday and they couldnt figure out why it would over heat. any help would be appreciated. Im selling this truck to a good friend of mine and dont want to let it go like that. It will only over heat when I go any faster that 70mph. should I get a t-stat from the dealership or are they all pretty much the same quality. Im flushing the radiator tomorrow and Dont know what else could be wrong. thanks in advance.

forgot to add that its back on a stock clutch and programming... so no edge on it right now.

 

Do you have a laser temp gun or something similar by chance?

Thing I'm wondering is if it's ACTUALLY over heating or just the gauge showing hot, does it show signs of obvious overheating? Smells? Boils? etc.

If you could check the temp of the rad inlet hose when the gauge is showing hot might tell you a little more what's going on?

 

No I dont have one of those. The only signs Ive seen is that the first time it did it I didnt realize it and the truck would not go past 80mph. thats when I realized it and pulled over. the other sign is that if I get on it for about 3-4 seconds that some noise that sounds like a fan of some sort comes on and will not turn off unless I go down to 60? Do these trucks have an electrical or mechanical fan? other than that, the truck runs good. just not over 70.

 

Hmm that is strange.

The fans on these trucks are not electric so it does sound like your truck is in fact running hot.

The fan has hardly EVER started on either of my tucks, happens only if pulling long grades in the summer or if I let the rad get gummed up with bugs, dust, dandelion fluff and general filth.

But I'm sure you have checked the very obvious things allready, like the rad is good and clean and you are topped up with plenty of coolant?

Like wise that the Serpentine belt is in good condition?

If all the obvious things check out ok, and the thermostat has allready been replaced. I would likely try a coolant system flush, failing that I would suspect water pump.

 

Sounds like an air bubble in the cooling system to me. They can be tough to get out sometimes.

 

It could be an air bubble. Im going to take it in right now and get it flushed and hopefully that will work. thanks

 

Maybe suction from the water pump is causing the lower radiator hose to collapse. This is very consistent with overheating at only higher sustained speeds. Does the hose look thin or feel weak? Is there an internal spring that could be missing or out of position? I'm not sure our trucks even come with one. Better yet, let the squealer deal with it, unless you're out of warranty of course.

 

Possible stuck thermostat or air bubble due to a leak. Most leaks are on the passenger side bottom of the heat at the heater hoses. Also, the fan is electrically controlled via the ECM. It has an electrically engaged clutch.