There really is no pressure. Its just a reservoir. It holds fluid. Its constantly being circulated so its splashing around, that's all.

I think you still have air, and what your doing is purging the air so the fluid level keeps going down. If you only put in 3 quarts after running the system dry, you are probably about close to having it full now. After I completely drained my system on my 88, I put in close to 4 quarts.

88 4R, 350 V8, R150 5 speed Sold <...uot; />
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride