I did mine differently...

On the engine expansion tank (now no longer the high point in the
system) I installed a 14 lb radiator cap, replacing the 7 lb cap. Then
at the high point in the system (approximately...) I installed a small
expansion tank (from Summit Racing, but could have been from anywhere),
and put the 7 lb cap on it. Air collects in the tank (a little is
necessary to accommodate the expansion when the coolant gets hot), and
the engine expansion tank is now full to the brim.

This cost more than your approach, but it doesn't have any moving parts...

bob



Glenn Ashmore wrote:
I will go by Grainger this morning to pick one up. They are only about $7.
It is made by Watts Regulator so it is probably red brass but in a normal
engine room environment on the closed side of the cooling system it should
be OK. I will dissect it and report back.