How much pressure can a stock heater core take?

[OldDad67]

I'm going to add an Aluminum radiator to my 49 P15 Coupe. How much pressure do you think the heater core can stand? I'm thinking 4lbs would be about max. Any opinions appreciated, thanks in advance.

[yourpc48]

Hey. By chance I pressurized my heater core today to find, repair and then test the repair. I put a bike inner tube section with the air valve in that section on the hose connections and clamped it on. I put about 10-15 lbs on it. I have the type of heater that has a square loop and 2 fans. I has a squirrel cage for the defrost and a bladed fan in the front behind the little doors that direct the air. Heres a picture of my heater with the cover off exposing the core and my 12V fans. Hope this helps.

[Mark Haymond]

Just this week I blew the heater core on my Mopar Model 36 heater core while running a seven pound radiator cap and having a fan failure. But keep in mind the thing is over sixty years old. A pressure test will show you what condition your core is in.

[JIPJOBXX]

This is my next job to take the heater out and see why the fan is making so much noise!!!! It works great but makes a racket.