I just recently purchased a 1987 F-250, for some unknown reason the windows wont stop fogging up on me. Its not just the windshield either, its ALL the windows. I put the defroster on and it makes the problem worse. I tried cleaning the windows with everything from ammonia glass cleaner to anti fog wipes, to rubbing alcohol. Nothing seems to work. Any help on this subject matter would be greatly appreciated.

Thanks

 

I'm not sure if this is your problem. If your heater core has a small hole in it you will get excessive moisture from heater and defrost vents which could cause your problem. Usually you will smell anti-freeze when this happens.

 

This is EXACTLY what happened to me. It was the heater core, with a very small leak. It was an easy fix in my 89.

 

The same thing happenend to my GMC. You can also turn on the A/C and that will help till you replace the heatercore.

 

Not sure if this is true but i was told that if you need to buy some time in replacing it that if the hole is small enough you can put a small amount of pepper in the radiator and it will plug the hole for awhile. I've never tried it, can anyone verify that?