As it says in the title I have a 97 GC limited. Its not over heating goes up to about 225 or so. The problem is when I turn the truck off the coolant boils/bubbles violently back into the over flow. I changed the thermostat to a 180 and put on a new radiator cap and it still does it. Its to the point where the low coolant light is on. Anyone out there have any ideas?

 

The 180 thermostat is doing nothing. It should be a 195. Try a factory radiator cap. New does not mean good.

 

Ill try a factory cap. what else could be the problem? i have ran it without the cap on and the fluid didnt come bubbling out the radiator. i did fill it while running and after a bit it did want to come out but not with pressure just over flowed

 

Any huge clouds of steam coming out of the exhaust?

 

No smoke or steam? I can't figure out what it is

 

How old is the radiator?

 

What you are experiencing is "afterboil" cause by the release of pressure somewhere in the system. Most generally this is caused by a leaky radiator cap. A coolant mixture of 50/50 held at pressure shouldn't boil until about 255*.

OR, you're experiencing a "hot spot" causing temps to exceed 255* after circulation stops. This usually happens around exhaust valves or restricted flow in the head. With the engine running at full temp, turn off the key then turn it back on after the engine stops. Watch the temp guage and see if it pegs out at 260*. If it doesn't, you're loosing pressure. If it does, you've got hot spots.

 

I turned it off then back on and the temp didn't peg at 260. It didn't move at all. I can hear a slight hiss from the radiator cap. I'm worried its a head gasket. I'm not sire how old the radiator is. I've only had it about a month.

 

If it was a blown head gasket, it would be bubbling when cold and running.

I had that happen on an old Chrysler. After starting cold and driving about 2 miles, I heard a whistling from the radiator. It was blowing viciously from the overflow hose and the coolant was still cold.