One of our hummer h2 limos occassionally overheats, only occassionally. Bought it used with like 40k miles from another company. It ran fine all winter no over heating.

Now today it gets to 250 degrees we shut it down. Same thing last summer, maybe once a month it would get close to overheating. Today a/c in the front was kinda warm but cold in the back. Does this have anything to do with it? Also there isn't a coolant leak that is noticable as it parks in the same spot everyday inside. What do you think could be causing this? What can be done to solve this or help while we figure it out? We've had it to the dealer last year and they couldn't duplicate the problem nor figure it out.

 

change the thermostat and flush the coolant system... $0.02

since it only does it now and then I would suspect that your waterpump is still working correctly... and that your serpentine is fine and not slipping...

 

What Muddy said............................and fan clutch

 

good point Chris....

The next time it overheats.. or gets past the usual 210...

Turn the engine off (no offense)
Try spinnig the fan by hand.... if it moves easily... you are probably due... if it is stiff and hard to spin... you are probably still ok...

 

sounds like you need to replace the thermostat....its like a $5 part from autozone

 

Yeah....I concur!!!!

 

We have replaced the thermostat like 5 times. Last time we put a fail safe in it, so if it does overheat (remember its a limo and it does alot of idling at wedding and when 25 people are getting out) the thermostat will stay OPEN. Its not the thermostat.

Would it be ok to completely take out the thermostat for the summer only and put one back in, in the winter? Would this help?

But we have 5 h2's and this is the only one that has this problem.

What we plan to do is complete coolant flush, then install extra aux fan in front of the radiator, and 2 aux fans behind the radiator blowing towards the engine.

We put a new radiator and fan on the h2 last year, cant remember if we did the water pump. Could the water pump cause it? Last year we thought it was a leaky head gasket and we ran some sealant in there, and it didnt overheat since then because it didnt overheat all winter, then bam it did it again today.

Thanks for your help guys! Trying to get as many ideas to check as possible.

 

It could be a waterpump... but it would do it all the time I think....

Sealant in an engine is not a wise choice... it's like putting a band-aid on a hatchet wound...

You could very well have a bad head gasket... if it doesn't lose coolant though it's going to be harder to determine... The only easy way to check is to put a pressure tester on the radiator and idle the engine...

Check out the radiator cap also... it's not unreasonable that it is failing...

 

With a bad head gasket, he should be leaking and getting even worst gas mileage, also an smell too.
Rad cap is not a bad idea because pressure would have to build...
wow this is a good one for sure..

 

Heres what I have planned so far, tell me what you think:
1. 160 degree "fail safe" thermostate for hummer h2
2. full coolant flush, going to wash out the inside hoses with a hose
3. single aux fan I believe its 9 inches or 7 inches for in front of radiator on h2
4. double aux fan for behind the radiator to blow into the engine for engine cooling
5. Water Wetter, used to add into coolant of engine to help run coolant cooler, buy 2 bottles