what lb radiator cap w/expansion tank

[Saltshaker]

what cap is used? can I use a 18lb cap?
Jon

[FrozenMerc]

I run a 13 lb cap in my Mercury.  I can't speak to whether or not your system will support 18 psi or not.  Remember that extra 5 pounds of pressure is working on large surfaces of many dozens or even hundreds of square inches (expansion tank and rad tanks), and as such will generate many hundreds or even thousands of extra pounds of force.

[cleandan]

From memory most of the expansion tank radiator systems were equipped with 13lb radiator caps.

When choosing the cap pressure be certain to include the heater core in the equation.....I've seen a few of the heater cores get blown open after installing an aftermarket aluminum radiator supplied with 18 lb caps.