You didn't say which motor you have, so your question is a bit difficult to
answer.

If you have a system with a separate expansion tank, there is no bleeding
needed. The system will push the air into the tank by itself.

For systems with the integrated expansion tank, there is a screw at the top
of the tank next to the fill hole. Open the bleed screw and set the heater
controls to full hot and slowly add fluid until it comes out of the bleeder.
Tighten the screw and start themotor. Allow full operating temp to be
reached, let engine cool and check the level. Repeat as needed. (The book
says that topping off is all that should be needed.)

As for your coolant loss, you could be having problems. The M50 (the inline
6) motor has a place where the head likes to crack. If you allowed the motor
to overheat, odds favor the crack having been formed. The crack occurs
between a water galley (passage) in the head and one of the exhaust ports, I
recall the #3 Forward exhaust port as being the precise location but I'm a
bit fuzzy on it. In any case, the head must be pulled to see if you have the
crack. The head gasket can slos be a problkem area for your symptoms, and
the good news is that the head has to come off to see if this is your
trouble; so you can check two things at once. (I appreciate that the "good
news" is not all that pleasant.)

What happens here is that coolant passes into the exhaust stream in very
small amounts, and blows out the tail pipe. when the crack is small, you'll
not know that there is water vapor present in the exhaust, eventually the
crack can enlarge to the point of visible steam but I'd suppose you would
have serious problems at that point that you would notice in the lack of
pleasant driving qualities that you have come to expect. In any case, this
is why you can loose coolant and not see where it is coming out.