Anyone know what the cooler line pressure is on a 48RE?

I just installed a brass coupling (for temp gauge) in the hot line going to the cooler and the line was not prefectly round resulting in a leak. I took the line back off and really cranked on the compression fittings which seemed to work. I'm curious what kind of pressure is in that line and I assume it varies with throttle position/load? Are we talkin' 10psi, 100psi, or 500psi? I'm asking because if it still leaks I'm going to either solder or braze the fitting onto the cooler line and I haven't decided which one to use.

Thanks!