OK, the radiator was bad so I replaced it. Now I've figured out that if I completely close the radiator cap to the point where it clicks the truck will overheat in about 30 minutes from cold. Now, if I just barely turn it back before the point of clicking it doesn't overheat.

Think it's a bad cap or is it building up too much pressure?

Thanks

 

I would replace the cap just to be sure.

 

If it doesn't hold pressure the water can boil and cause over heating, if it does hold pressure then the temperature at which the water boils is higher so it doesn't over heat.

Change the cap!

Wayne

 

I'm kinda confused. I can drive with the cap completely off and no overheating. Wouldn't that = not holding pressure?

Thanks.

 

It would and that doesn't make since to me.

 

My thoughts exactly

 

Blown head gasket. Have a block check done.

 

This^^^ Been there done that!

 

I had the pressure test done before I replaced the radiator or thermostat. The mechanic said no signs of a leaky head gasket.

You know, I had a 1994 Taurus SHO. The pressure would build up in the gas tank and turn the automatic fuel shutoff switch down every week. All I had to do was loosen the capa bit to let the pressure out and always leave it there. Problem disappeared. Six trips to two Ford dealerships turned up nothing each time.

Is it possibly a "Ghost" problem like this?

Thank you

 

A pressure test and block test are 2 completely different things. You'd be surprised at what you can miss with just a pressure test. Have a block test done. You have a blown head gasket. A head gasket can blow where it only allows combustion gases to leak into the cooling passage when warm. Your symptoms are that of super heating the water due to steam. Get rid of the cheap chinese overflow cap first. Get a motorcraft and report back.