Re George's comment on bleeding air, this is not only important, it's difficult! I once changed the thermostat the day before driving our Pantera to the Fun Rally, 550 miles away. After thoroughly bleeding the system, I let the car sit overnight in my shop. Before leaving the next morning, I bled the system again, and got considerable air. We drove 6 hrs to 'Vegas without incident, and after cool-down in the covered parking garage a few hrs later, I bled the system a third time... and got more air. During the 3 day event, I bled it a 4th time from cold, and got only a little air. Just before we left for the trip home, I checked it yet again, and finally found no air. Ever own a water bed? Same thing: air sort-of dissolves in water and only slowly do microbubbles of air coalesce enough so they can be bled out.
FWIW, I use a $25 Lisle #22150 system to do this: it is a 2+qt funnel with various adapters to rigidly clamp the funnel to a tank opening without leaks. You fill the system thru the funnel until about a quart is left in the funnel during initial bleeding. Then start the engine and let it idle until the thermostat opens, whereupon air burps out thru the funnel; the excess coolant will then drain from funnel to inside the system. You'll need to add more coolant at this time- up to maybe a gallon more! Shut down the engine and re-bleed.
Note- all this time, the rad-cap is off the tank and some extra coolant is always in the funnel to keep air from being drawn in. A stopper w/handle is provided for funnel removal without spilling excess coolant. A full description is in the Oct 2001 POCA Newsletter (POCA website Archives at www.poca.com). No tilting of the car has ever been found necessary with the Lisle attachment. Recommended!