overheating problem

I have an 02' sporttrac and they other day it started to overheat while towing a small trailer and having the a/c on. When we stopped there was coolant coming out of the radiator at the plastic plug on the lower passanger side. the next day I started it up to see if it would do it again and after running it for quite a while it never leaked or overheated until i turned on the a/c and revved it up to 2 or 3 thousand rpms. I am at the moment wandering it maybe the thermostat isn't somehow closing or maybe a hose colapsing under the pressure but not sure. Also when it did finally overheat the second time I heard a farely loud click come from the engine bay just before the temp shot up. thanks for the suggestions.

i dought a thermostat, are colling fans coming on properly
btw whats a sporttrac ???

sporttrac is a ford explorer.

hello bain,how many miles on engine have you checked fans possible wp,hows the condition of the cooling system??if its high miles make sure its curculating properly.i (my son)has a f-150 with 247k i just replaced wp(original) the propeller rusted away!!!also make sure clutch fan it working
Good Luck & let us no
btw what engine do u have??

What does the coolant temperature gauge read at the time of the overheating? Have you had the cooling system cap pressure tested?

I too doubt that the thermostat is the problem. Even if it were stuck closed, you should experience overheating without the A/C on. And a hose should not collapse when under pressure. Since there will be pressure on a system with a properly functioning cap, or as it starts to boil the coolant, you'll tend to experience hoses bursting rather than collapsing.

You may want to install a new fan blade clutch. There are tests for the clutch which require a "digital photoelectric tachometer" similar to a timing light.

-Rod

It could be a thermostat but check the water pump also. You could have a pluged hose also. As to the "click" you hear could mean that the fan clutch is malfunctioning. But it shouldn't heat up quickly