[Excaliber]

Well thats news to me!! I've always just walked into the auto parts store and bought whatever cap of the correct pressure they laid on the counter. Said caps have always been able to draw the fluid back into the radiator from the overflow.

I've never seen any radiator cap that wasn't capable of drawing the fluid back in? So Pat, are you saying YOUR cap does NOT draw your overflow fluid back in when the engine cools?

Come to think of it, I always specify a manual pressure relief type cap, one I can lift the little handle on and release pressure if I choose to. Perhaps that is the difference, as opposed to a cap that the only way to release pressure is to turn it to take it off. I always considered those a dangerous type cap and never use them.