i konw there can be a lot of diff things that can cause a truck to overheat but here i go... i have a 02 1500 2wd 5.3 and i live in houston so it gets HOT and HUMID and that is an understatement!!!! well today i was at the jack in the box and my temp got to about 230-240 when it gets that high i put it in neatrul and rev the rpms to about 1.5K to 2K and the temp goes back down to about 190 -210... i replaced the fan clutch last summer and put a ac delco and it still did this but it's been a very chilly winter so i have not had to worry about it until now... any suggestions? i have flushed the coolant system before but not the thermostat but i will prob do that this weekend... i have no codes truck runs like brand new just wants to overheat. truck has 157K btw. thanks for any input

 

From your explanation the only thing that gets affected by sitting still and reving the engine up is the fan and the water pump spin faster. If you have ruled out the clutch by replacing it I would be looking at the water pump. I have seen them over time corrode on the inside and the impeller loses some or all of it's pumping ability. I would probably install a new thermostat too with your mileage. Does it only do this when sitting still? I would also make sure your not losing water somewhere. When the temp gets that hot and then drops that low rapidly it is usually an indication of a low coolant level. I would definitely check it out ASAP...a cheap part can cost you a blown head gasket or worse. Let us know what you find.

 

well i have replaced the water pump before the only thing is i didnt do it my dad did and i dont know what kinda part he used... i know they go out often on these trucks... and yes it ONLY does this while sitting still, it never ever goes above 210 while driving... there was a point in time when i was looseing coolant and had to refill about every 2 weeks... but then my friend had this bright idea to get that gasket sealer that you put in the coolant and crush that up and that fixed that... iunno if maybe that could be causing this cause im not sure if it was overheating before then, but im pretty sure it was.

 

I would definitely start by making sure you are not losing coolant. I am not a big fan of the gasket sealer stuff (mechanic in a bottle) either, but I guess some of it does work. If you have a radiator shop nearby they should check yours for free to make sure it is circulating properly or you can remove the cap when it is cold and start the truck to let it reach operating temp when the thermostat opens and see how the water circulates in there. If it isn't circulating right you either A: have a partially clogged radiator or B: have a weak water pump. The fact that you say it only occurs while sitting still makes me think the fan or fan clutch is bad though. Check both of those.

 

I say waterpump.....sounds like the impeller is starting to loosen from the shaft (inside the pump).

 

I would probably say a waterpump is starting to leak. Check for signs of coollant residue on or around the weep holes or around where the hoses connect to the waterpump. Speaking of this thread I should check on my grandmothers truck too seeing it was using water last summer and now that it is getting hot in H-town again. What part og H-town are you in?

 

i live in the pearland area... ill check how everything flows tom and i know for sure that the waterpump is not leaking.... the it can not be the clutch cause that bitch is brand new and like i said it did it right after i changed it anyways... what would i be lookin for on the fan? like cracks or if the blades are loose?

 

I think there's a good chance it's the radiator. Putting that sealant in there quite likely clogged it up and you're not getting good flow. When you're moving, you get enough airflow to keep it down but water flow alone is not sufficient. The suggestion to take it to a radiator shop is a good one. Good luck.

 

Do you have a Heat gun that measures temperatures? If so check your temperatures... possibly a faulty sensor?

 

Have the radiator shop put some psi on the cooling syatem to easily make the leak more noticeable. That leak can cause air to enter the system and thats what happens when the temp goes up and down like a rollercoaster. Even if the pump aint leakin does not mean its not bad. Its just a matter of taking stuff apart to check. But get it checked for a leak first.