Getting Fuel in cooling system-Power Stroke

Each time after running engine and letting cool down, when I check cooling system I find approx. 1/4-1/2" of fuel in the radiator. ANY ideas?
This is a late "90's vehicle.:headshake

Most likely cracked head (s). Slim chance of injector cups/ injector O rings failure.

Late comer, sorry. I would figure out some way to put some REGULATED air hose pressure in the fuel rails to isolate it. If you are doing the work I would def. advise low to high difficulty. Orings - cups - head. Would sure suck to yank a head and find a 10 dollar oring kit is all you needed. Theoretically the fuel/coolant should never see each other, that is the whole idea of the cups, but stranger things have happened...