The past couple of days the Coolant temp has been running WAY past normal (230ish) at idle,once I get moving its fine. Also when this happens the AC quits blowing cold. Granted, it has been hot here 103*-106*(113* on the mirror). The truck is bone stock. I've checked the clutch fan and it feels pretty stiff (seems to blow hard with engine running)so I'm assuming its doing its job?? Thought about installing a 180 t-stat(although that doesnt seem like it would be the problem).My WS6 has a 408ci LS1and it runs 185* ALL the time with the AC on in this heat!Any input is GREATLY appreciated!

 

More info please: Year and miles, have you done a lot of towing, does the transmission shift out smooth, and any lights/dash indicators other than temp readings? Thanks.

 

IF it was me, the first thing I would do is check the thermostat and see if it's working, actually just replace it. They are cheap enough. Is it still under warranty? Did you check your coolant levels? It's a bit odd the AC would stop working when the temp goes up.

 

It is a 2003 H2 with 58k miles. No lights on, tranny shifts great, no towing,wife drives it a couple of times a week. Coolant level is fine,It is out of warranty. No issues to date exept for this. Logic would tell me that it would have to be the fan clutch or t-stat, but logic isnt always right! Thanks.

 

how long are you sitting for? in excessive heat, sitting in one place is going to heat up your coolant pretty quickly since the fan is the only thing pulling air throught the radiator. what is your tranny temp running? does it match the engine coolant temp? if it drops back down once you start moving, it's not the thermostat, it's either open or closed, there's no middle ground. a cooler thermostat wouldn't make any difference, especially in the heat you mention. have you been through a lot of mud with it? mud clogs the radiator fins quickly and will have a lot to do with running hot if you don't pressure wash it clean (i learned the hard way). if your tranny temp is staying below 200 and your engine temp is hot, it could be the sending unit, but that's doubtful based on what you're describing. if it starts heating up from just stopping at a redlight or something, that would lead me toward the fan clutch or water pump. of course, it could just be low coolant, since you didn't say if the reservoir was full or not. lots of questions, but if you're under warranty, the dealership is the place to get the answers.

ok, so you responded while i was typing. i'd say fan clutch or water pump. what's your tranny running?

 

Have you ever serviced the radiator? I'll bet you got "slime". If you bought it used, you may not know trailer towing HX. Have a reputable shop or dealer do a flush, or do it yourself and I can help with questions on what to do.I would start with that, and if it does not improve, look at the next possible cause.

After the flush, put in RED LINE Water Wetter as the last pint

 

When you pull away from the stop light with the engine temp at 230 you should hear the a lot of noise from the fan if the clutch is actually working. If not, it's junk. If you let it idle in the driveway and it gets to 230 pop the hood and watch the fan as you shut off the engine. It should stop almost right with the engine. If it takes its time coming to a stop the fan clutch is not engaged and it should be with the engine at that temp. Let us know what you find.

 

Thanks for the responses. Yeah the tranny temp is close to the rad. temp. No mud, never seen a dirt road! Gonna try a fan clutch tomorrow. Coolant is full and was flushed last year.Thanks again, I'll post how it turns out.

 

One thing if you're doing this yourself, some fan clutches are threaded onto the water pump nose. If so it will be opposite the direction of rotation so the thing would drive the fan clutch on against the resistance of the fan itself. Meaning it's probably a left hand thread. Also it will be a bear to break loose without some sort of impact. The guy who did mine the last time used an air gun with a pointed set against the hex shaped part where the clutch threaded on. Otherwise leave the belt on and try a wrench and see what you can do. Good luck.

 

Got it off a while ago,big cresent and smacked it with a hammer, spun right off.
Had to put one on my Cummins a couple of months ago...Hummer was MUCH easier