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Over heating

We changed the thermostat out with a new one and the fan clutch,and now it runs cooler than before…but, now after its been driven for about 10 miles or so and you pull over anywhere and let the truck idle (i.e. tacobell drivethru) the temp will start to rise and after about 2 mins it will be overheating,if i pull over and shut it off for about five mins and restart it and leave, it will go back down to normal and will not rise again even when idling with the a/c on. Once it starts to overheat from an idle the temp will not drop to normal if i get out and drive it will stay in the red,only if i shut it off for a couple mins then drive away, it go back down.What are the chances the waterpump could be bad also, and can anyone give any info on this that would help us out, thanks

I’ll bet it is the cooling fan clutch. The fan is mounted to a clutch that is supposed to regulate the speed of the fan based on the temperature radiating from the radiator. If it is not, there is no air being forced through the radiator, and it is not cooling at all.

Is it REALLY overheating or does the gauge just read high? Have you checked the actual temperature of the coolant? Shutting the engine off for five minutes is not enough to cool it if it really is overheated.

Are you sure there are no air pockets in the cooling system? I’d also check the coolant temperature sender.

If it idles sometimes with the AC on and doesn’t overheat it should idle anytime and not overheat. I suspect it’s not really overheating. Does it boil over? You didn’t say it did, you just said the gauge was in the red.

We bled the lines only by using the bleed screw,isnt there a more affective way to do it to be sure?

When we checked the coolant temp after shuting off the engine and letting it set for about five mins and i dont recall what the temp was but it wasnt over 195 deg. So should we check the temp after the engine has stared to overheat and the coolant is trying to boil over and record it? It wansnt overheating when we checked the coolant temp, the needle was about 3/4 up the gage, 145 deg is ringing a bell but im not positive.

This morning on a 3 mi trip to school it went from setting overnight to 3/4 up the temp gage in less than 2 miles and was slowly rising after that, after we shut it off and sat at the school for about 10 mins the needle was back down to about 1/4 up from cold and after 1 mile from school on our way home at 45 mph it was in the red, and was all the way home…could it mabey be something electronic? Its strange that it would rise that rapidly after setting all night, thanks for the input so far

I have the exact same thing going on it sounds like. My truck was overheating pretty quickly and I changed the therostat, but that didn’t do anything. The repair shop that did the therostat said it needed a new radiator. I didn’t do it and took it home and flushed the hell out of it which did about a 50% job. It has been wroking for now, but if I do any big grades or hot weather driving it is running close to blowing it’s top. I think I am going to have to do the radiator.