Coolant Question/Radiator Caps

[tinyelvis]

Ok, I have always wondered about this and it's about time I asked. Normally I'll go to the auto parts store and say I need a rad. cap for whatever car and they get me what I need, for the most part..

My question is this: Why do certian ones have certain pressures, do it matter what size your engine is, or how hot you want it to run, not overflow, etc etc.. Anyway.. please clear this up for me if 'ya can!

[stealthcruiser]

666 posts.
increasing the cooling system pressure raises the boiling point of your coolant.
don't put too high of pressure cap on an older cooling system not designed for said cap,unless you know the condition of all cooling system components(to include the expansion,or "freeze" plugs),
don't ask me how i know!

[C9]

StealthCruiser is right.

A 15# cap raises the temp to 257 degrees F. before the coolant boils.

I ran a 15# cap in my 32 with 70 Buick 455 engine and Walker radiator.
About a year down the line I popped a seam.
The radiator shop that fixed it recommended I run a 7# cap.
I put the 7# cap on and it works fine.
I have an overflow tank as well and since it takes a radiator cap, I bought a new one and removed the spring loaded pressure part of the cap and now it's a simple rubber gasketed cap.
The way the Moon water recovery tanks are built, a regular pressure cap will block off return coolant flow.
Seems like a lower rated cap on the recovery tank should work, but it does better with a plain cap.

The 7# cap raises the coolant boiling point to about 234 degrees F.