Overheating, no heat, coolant loss, blah blah blah
 

Have a 2002 Tahoe 5.3L, initially began overheating ONLY when ac was on.........now all the time. It has never had heat .....long before overheating started) and now it's losing coolant from somewhere.....no indications of a significant leak. Im assuming its just blowing it out when driven....oh yeah, fan clicks on and runs okay........

*You are correct in your assumptions that I don't have even the most remote iota of a clue as to what I am doing, but I do want to at least convince my husband to replace the thermostat, which I KNOW isn't working or isn't there (mechanic told him this awhile back, but I cant remember which it was).......I believe he is resistant in doing ANYTHING because, well, Im female and God forbid.....

By the way, does anyone have factory service manual for this model/year? I'd give up an appendage for a link to an actual FREE FSM



Preemptive thanks to anyone willing to help me troubleshoot

Sounds like the cooling system needs a complete check. If overheating I would check the coolant level, change thermostat and check for leaks. Could be the thermostat is stuck closed or partially closed. Does turning on the heat help lower the temperature? Do 'you have heat? Check all the hoses and clamps for tell-tale signs - might be dried coolant stains. Check the ground underneath for stains. Does it overheat at idle or only at speed? If it only overheats at speed and is fine at idle I would suspect a clogged, scaled up radiator that has lost the ability to effectively remove the heat.

i know in my 02 the heater core was leaking. its contained on the inside firewall on the passengers side. it was a work truck so it had a vinyl floor mat. we could never actually see it just i would be able to smell it and the heater really didnt work. you have to take the dash apart to get to it so i traded the truck in lol. also the heater wont work if the coolant isnt full.

To find the leak, can get free loaner kit to pump up coolant system pressure, to make leak easier to find. This may be the cause of all the running hot and lack of heater.

Or take to an independent ASE mechanic shop.

Welcome to the forum. If the thermostat was missing, it would not heat up at all. It's possible the thermostat may be stuck shut.

Okay, so oddly replacing the thermostat was a HUGE deal..........unable to find one that actually fit,.....the correct part number absolutely did NOT fit.......apparently a different water pump was installed at some point.. Finally got thermostat dezalt with and sure enough, its still overheating. I am right now, flushing the radiator............3rd flush produced some fairly big chunks of rust and gel like substance which I am assuming is from previously mixed coolants. I cannot believe the can of worms I have opened.

But thank you to all the replies, this definitely helps!

Yes, if I turn on heat it does help lower temp, especially when travelling at higher speed. Thermostat was actually bent but still opened in hot water.......finally got the right part for it bc "correct" part number simply didnt fit, no matter how much cramming was tried......

Your radiator just might be have too much calcification/crud, and might need to be replaced. Such overheating was why I had to replace the radiator in my 1988 Mazda truck, poor little radiator just couldn't handle our Arizona heat any more.