I’ve got an 02 GMC Sonoma. Last summer the truck started overheating, but only when I am backing up with a load. (I have a small boat and pop-camper.) As long as I am moving forward, there is no problem. As soon as I start to backup, I can watch the temperature guage climb, and if it is really warm out, by the time the camper is in the spot, or the boat in the water; I can hear the cooling system boiling.
I replaced the thermostat last fall, and have verified the fan is turning.
I am wondering what I should ask the mechanic to check?
Thanks:
This engine probably has a thermostatically engaged clutch fan. Have the mechanic make sure the fan is engaging when the radiator temperature gets high. When the fan clutch is not engaged the blades will turn but not as vigorously as when the clutch is engaged. These fans make a noticeable roar when they are truely engaged.
Hope that is what it is.
The first thing to check is the condition of the tranny fluid.
Tester