My F-150 Overheats when I drive at high speeds with the A/C on.
History:
97 Ford F-150 Super Cab
105,000 Pampered Miles (Original Owner)
4.2L V6
Nov 2004 used a Radiator Leak fix solution
In the last month I replaced the Thermostat first from High temp OEM to Medium temp 180 degree
Then I replaced the fluid 50/50 after using a Prestone flush solution (Found Globs of Radiator Leak fix solution)
Then I replaced the fan belt
Then the fan cluth
I also cleaned the front of both of the Radiators and between them because it was a little cloged with road debris.
I thought that I had it beat but....
I just drove 300 miles to go camping and could not use the A/C because it still wanted to overheat. Not fun in the Southwest!

I guess I will try the waterpump and radiator next, any ideas?

 

Hi and welcome to the forum

Does the temperature gauge go the whole way to the top when it overheats? Does it blow coolant out?
4.2L engines had head gasket problems that sometimes looked like an overheat condition.
I've also replaced radiators for the same problem you're having though too.

 

Yes, the guage goes all the way to the top and it will blow out coolant. If it were the head gasket wouldn't it overheat with the A/C off? Also, no oil/coolant mixing...

 

Yes, typically if a head gasket was bad it would have the problem all the time.