Test out FGT's theory by driving the truck a few times, checking the level after it cools down each time. If you are running cool, theory seems quite reasonable.
The normal level in an A-D truck's radiator is about two inches below the top.
Be careful with putting in a high pressure cap in a 47-53 1/2 ton truck's cooling system. The standard radiator cap was 0 psi and some parts in the system might not handle a pressure cap. A 4 psi cap, as used in 54/55, might be OK.
