My car has been overheating recently, only after driving quite a distance and then idling for a while. I looked at my old rad cap, and the rubber was fairly brittle and chewed up - the center portion of metal was a brownish color rather than silver. Probably the same cap that came w/my CRX in 1989.

Bought a new honda cap ($15) and threw it on. Car's temp stays lower now, hasn't overheated yet. Could the bad cap have been the entire cause of my overheating? If so, please explain - I know it has to do w/pressure raising the boiling point, but explanation never hurts, right?

Thanks -

Alex

 

The boiling point is raised about 3 degrees per lb. of pressure. The cap is suppposed to hold a certain amount of pressure. If it overheats past that point it will release pressure to the overflow. When the system cools the drop in cooling system pressure draws in water from the tank.

If the cap doesnt hold pressure the boiling point is reduced. What may be a normal operating temp. can be too hot if the pressure isnt held. A cap that doesnt hold pressure wont allow the coolant to be liquid at temp. Steam has no cooling capabilities.

 

Cool, that is sorta what I figured out. The old cap, being brittle and chewed up, would let coolant past the cap's seal into the line to the reservoir at a lower temp, and this is why when I overheated coolant was coming out of the reservoir, and I did NOT see steam. Thanks!

Alex