Hummer h2 limo occassionally overheats

[SummitUp]

Originally Posted by pteam

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?

The primary function of the thermostat is to allow the engine to warm up quickly from a cold start. But it also performs an important function of controlling the actual flow rate of the coolant through the radiator (by creating a restriction). For optimum cooling the coolant needs to pass through the radiator at an optimum rate to allow it time to release or "give up" it's heat. I've seen situations where removing the thermostat actually makes the situation worse because the coolant moves through the radiator so fast it doesn't have time to exchange or release all the heat it could if it were moving through the radiator at a slower rate.

Originally Posted by pteam

Last year we thought it was a leaky head gasket and we ran some sealant in there.

Adding radiator stop leak in an overheating situation is definitely contra indicated. Besides stop leak being nothing more than a temporary band aid for a leak somewhere in the cooling system, it can tend to clog up the coolant galleries running through the radiator and diminish the cooling efficiency even further. I would definitely flush the system and get a <tranny cooler> making sure to bypass the ATF lines going to and from the radiator so at least the heat from the tranny won't be dumped into the radiator.

edit: I should have asked: What is the temperature reading on the tranny temp gauge when your overheating. Also, (a very remote possibility), you may not be overheating at all, but rather you could have a bad temperature sensor sending bad info to the temp gauge on your dash. I've seen it happen...