I have a 1120 cubic inch radiator on my F250 460 Ford. The block should hold approximately 3 gallons, the radiator, about 4., however, when I open the petcock, take the cap off, and take the lower hose lose, I only have approximately 3 gallons of water/coolant drain off... How do I insure that I am getting most/ all the fluid out, because, according to my calculations, I am only draining about 1/2 of the total fluid out!?
How did you calculate the radiator volume - if you took the outside dimensions you massively oversized the answer.
Radiators use small tubes : approx 1/8” diameter to maximise the water tube in contact with air and improve heat transfer so the water volume in the radiator is some 10 to 15% of the space it occupies.
10 to 15% is a guess but you get the idea.
Another example is a solar thermal panel : 2m long, 1m wide and the channels are so fine it only holds 0.5 litres of water - basically a pint - does depend on the manufacturer though...