Electrolysis? If it is not a head gasket. I have seen cylinder liners eaten through until there are pin holes in the cylinder wall. I have no idea why it seems to happen predominately in Ford equipment. I have been given a thorough explanation, years ago, and there is no way I could recite it now.
I would drain the engine oil, leave the drain plug out. Top-off the coolant and pressurize the cooling system with a pressure tester. If coolant is leaking into the crankcase you will see it come out of the oil drain hole. The only way to confirm if it is a head gasket or pin hole in a cylinder liner is to remove the head and inspect the head gasket. If there are no apparent tracks where coolant was passing into the crankcase, you'll need to get the head checked for cracks. To check if it is a cylinder liner you will have to remove piston and rod assemblies. The pin holes typically happen below the top of the piston when it is at bottom dead center. You could skip pulling the head and pistons by pulling the pan and pressurizing the system and looking to see where the coolant was coming from, rotating the crank so the bottom of each cylinder is exposed. Either way is a bit of work.
Brian
