I've heard about the cardboard trick though, to prevent air-flow. I might try that. I thought it was odd though because it never had any issues in warmer weather. And the radiator cap? I never thought of that, how come?
I had to do the card board thing on a Dodge Avenger. The T-stat broke, the round disk broke free and turned sideways. I just didn't have time to change it right away.
My sister had an old Comet that would not generate any heat. This was before I really knew anything about cars. The guy at the parts store said to change the cap, it needed pressure (pressurized water can get hotter before it boils) to be able to generate heat.
I thought he was full of crap, but I tried it because it was a cheap part. I was surprised when it worked. I have since heard that radiator caps are generally only good for a year or two before they start losing their pressure rating.
I feel, the part is cheap, easy to swap, and really can't hurt to try. Just my 2 cents worth.
