What pressure radiator cap?

[AB6DO]

Finishing my 1948 3100 5 window 5.3/4L60E conversion. Runs great, cooling so far great. I used the original radiator tanks (in perfect condition) and 4 row brass core. What pound pressure cap would I use with this setup. The engine is a 2007 Classic, stock water pump and thermostat (188 degrees).

[joedoh]

if you use a pressure cap be certain to have a recovery system, the factory radiator just has a puke tube. you will need an expansion tank that feeds from the rad to the bottom and keep coolant in it, as your pressure cap opens to release air (at first) or coolant (as expansion) it will go into the recovery tank. then as it cools down the recovery tank will allow the radiator to "refill" from contraction.

do not use a catch can, that only lets coolant out and doesnt pull it back in.

most GM systems are 16lb.

[1project2many]

I would limit maximum pressure to 14 psi. With 50/50 mixed coolant you have boil-over protection to 250 deg F. Caps for a recovery bottle have a gasket in the top as well as under the spring. Without the gasket your recovery tank is only a catch-can.

[mr48chev]

I think you can get away with a 14 lb cap with the 4 row brass core but what did your radiator guy who did the radiator say?

Stock AD radiator with honeycomb core runs a max of 4 lbs.

[capnduane]

Nice truck! What about your heater core? If stock, what can it hold? I am running a 7lb cap, and recovery system on my '55, and it works fine in the 106deg heat here in So Cal. Fresno is hot in the summer too!