Quote Originally Posted by roverv8 View Post
I have a 1988 RRC with a 4.6 in it, has the bigger 3.9 radiator also,

When i brought the vehicle it still had the old type overflow tank with a 7 PSI metal type cap,
I found it was pushing coolant past the 7 PSI cap via a coke bottle on the overflow hose,
so i tried a 15 PSI as per the plastic screw on type which is on the Later expansion tank.

Still no good, losing coolant, so i fitted a new large plastic expansion tank with a new 15 PSI cap and bottom rad hose to suit.
still using coolant, unfortunately in the end i had to do the head gaskets.

Moral of this story is, i never do the 15 PSI cap right up tight, just do it up a little firm hoping to achive around 7 to 10 PSI,
It doesn't use or force any coolant out at this either
I should add,
My radiator had been rodded, a new thermostat and the viscous fan working correctly