The maximum pay load is 3534 lbs (3.5 tons ) and the maximum towing capacity is 18000 lbs or 9 tons
from your description of 2 thermostats I take it is a v8 hopefully a 6.6 ltr v8 turbo diesel
it should have come with a 6 speed allison auto transmission.
with a 35ft, 5th wheeler behind it the combined gross max mass would be getting close to max allowed
add any speed on the highway and the transmission will be running at high oil temperatures and that heat is transferred to the radiator by the transmission oil cooler in a tank of the radiator
the high oil temps could be slippage in bands and clutch packs in the transmission( not noticeable under normal driving conditions) so an check and adjustment would not go astray
next if the adjustments are set properly, it may become necessary for you to consider an air to air transmission cooler so that the heat from the transmission is transferred to passing air flow and not accumulated and added to engine coolant temperature
those kits are available from most accredited transmission specialist shops and will reduce the transmission oil temp by at least 40%
taking that the coolant temp is 95 -98 c the transmission oil will be running a lot lower, saves the oil and the transmission and will help prevent boiling of the coolant
it may be necessary for you to lock up the fan clutch as well
SOURCE: 2002 GMC YUKON COOLANT KEEPS EVAPORATING
Sounds like a head gasket to me. Turn the engine on and put your hand near the exhaust and see if you feel any moisture. If you feel or see vapor it's more than likely the head gasket. Although it could be the intake gasket as well. Either way you're looking at a lot of work.
SOURCE: Replace the thermostat on 2002 GMC Envoy
4.2L Engine the thermostat and the neck where the hose goes on is one unit $25 at autozone
SOURCE: 1994 gmc sierra 4x4 350cu inch auto trans engine coolant gurgling
I have seen this many times before. The sound is air being forced out of the radiator cap and escaping back into the coolant recovery bottle. It can be as simple as a new radiator cap or as costly as cylinder head crack, or even block cracked. It is important that your radiator be completely full with proper coolant mix and have a good working order cap with the proper pressure.
SOURCE: 2005 yukon denali is overheating
Start it cold with rad cap off, and heater on high heat, and let it run until you see increased flow in radiator, indicating thermostat opened & engine reached operating temperature. Rev engine slightly every once in a while and hold it there for 10-20 seconds, just to help purge air better/faster. Watch rad flow again, and wait until you see increased flow 3 or 4 times. Then top up coolant in rad to an inch or 2 from top of rad, and put cap back on. Top up return bottle to appropriate level on bottle & then try it again. If it still heats up, get back to me. Does it overheat at all times? Rad fan is good i take it?
SOURCE: 2000 GMC Safari Overheating
double check the pump the impeller inside can be rotted away and it will still pump some but not enough to cool it at 65 mph , you can remove the pump and take off the plate on the back and look at it easily? second get a tech to loan you his infared thermometer and double check the temp it can pinpoint the problem ? good luck [email protected]
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