As a suggestion after a full flush, 1)hook the garden hose up to the water neck (no tstat) and let her run for a while. Compressed air is nice but not essential. Get it really well flushed 2) Drain block as best you can. 3) Assemble 4) Add the correct amount of 100% antifreeze first. As posted above, a 16 qt system would take 2 gallons of 100% antifreeze 5) Top off with water. 6) Run it to mix well.

Doing it this way gets enough antifreeze in even if there is water left in the block... which there always is. I have always had good luck with Prestone extended life antifreeze or similar.