radiator cap psi. have question please read>>>

[cmansturbomx6]

ok the radiator cap on my car says 13psi. on it and my haynes manual says that the rad. cap should be 15 psi opening pressure. first of all is the 15 psi correct and secondly how much of an affect would the 2 psi. difference be on the cooling system. also what would the affect be if i were to put a lower psi cap and/or a higher psi cap. any info is greatly appreciated!

ps. i have an 88' atx gt

[Dyoel182]

Higher pressures raise the boil point of the coolant which means the coolant will get a little hotter before it boils over. The higher pressures can be a little harder on a cooling system expecting a lower pressure. Everything for our cars I've ever seen has said 13psi cap.

[fredio54]

if you are a maniac, or live in a hot place, higher is probably better. the only thing it will do, is show up leaks that were borderline already. nissan use a 0.9 on NA motors, and a 1.2 on boosted ones, i use 1.2s because i have a similar effect on engines as a turbo ;-)

so far as boiling over is concerned, it isnt so much about that, thats what the overflow bottle is for. its more about controling hot spots inside the head.

[cmansturbomx6]

i was under the impression that if had a lower psi cap than what was recommended that it would decrease the pressure in the cooling system therefore the cooling would be a little less effective, where as increasing the cap psi. would increase the pressure in the system therefore making it cool more effective. I know you can't go to high or low but i was just wondering if the 2 psi. i was referring to in the previous post would make a difference in the cooling capabilities.

or am i thinking of this backwards?

[Dyoel182]

It would make a difference yes, but I have never seen a 15psi cap.

[fredio54]

higher psi = capable of cooling the car better under more extreme circumstances, day to day it will make little difference, if a leak shows up, it'll be sooner with more pressure.

[cmansturbomx6]

thanks everyone i appreciate it