ok here is the problem i am having my 01 z71 5.3 is overheating when the A/C is on and the truck is in park or at a light to long. when i start moving the temp goes down to normal temp like it is suppose to. i have already replaced the thermestate,and coolant temp sending unit and flushed the radiator (yes he resevior is full). i was planning on changing the water pump but im not sure if that would fix the problem any help would be greatly appreciated. also the truck is a 2001 with 219,000 miles on the factory motor still with great compression and going strong.

 

Does it still have the clutch fan on it? The clutch could be bad and not locking up the fan when it heats up, so it would not pull enough air at idle to keep it cool.

 

CHECK THE FAN CLUTCH LIKE kbracing96 SAID AND ALSO CHECK THE HOSE AND THE NIPPLES OFF THE RADI. WERE THE HOSES SLIDE OVER THE SMALL HOSE THAT GOSE TO THE OVER FLOW JUG SOMETIMES GETS STOPPED UP AND CAN CAUSE THIS.

 

nope. at an idle, it won't pull enough air even if it was a direct drive. try a pressure test on the system and see if you are loosing pressure. if you are, then find where the leak is. i had an issue like that with my S-10 years ago and finally found a pinhole leak in the top of the radiator under the shroud. also, your "radiator" cap could be going bad as well, no pressure = overheating. is it the original radiator? if so, you may want to take it to a radiator shop and have them clean it.

 

I had the same problem on my older truck i use to own and after replacing the thermo, water pump and a whole bunch of little things it ended up being the radiator. Once that was replaced it stayed nice and cool. Got a new one from a junk yard that came out of a brand new wrecked truck for $75. Good Luck on solving your problem

 

What? That's how a clutch fan works. When setting at an idea, it heats up the little spring on the end of the clutch because there is no air flow cooling the radiator, and then engages the fan clutch making it direct drive to pull enough air through the radiator to cool the truck, then when you start driving and get air flow thought the radiator, the spring is cooled off and the clutch let the fan free wheel as to not take up unnecessary horse power. That is exactly what he is describing. If he has a leak, then it would heat up because there is not enough coolant to circulate and cool the engine, but it would NOT cool back down when he started to drive it.

 

thanks everybody i will try the fan clutch or i will just buy elec fans if that don't fix it i will upgrade the radiator.

 

99.9% sure it is going to be the fan clutch

 

go out and try to spin the fan clutch.If it spin easy it is the fan clucth.If it is hard to spin it is alright.

 

It could also be a stopped up radiator.

I'm also gonna put this in a better section to get some more opinions.