i have a 1980`s 120g with a 3304 motor,i have coolant in the oil pan,no oil in coolant,not burning coolant and cooling system will hold pressure when tested... anyone see this before???? water pump,head gasket,liner seal,cracked block??? i dont understand how system could hold pressure with a leak this big 3 gal in one day!!!
Check the weep hole on the water pump they get plugged with dirt if it is wet there try that first my gut tells me liner seals or clavation erosion on a liner in your case engine would have to come out if it is liners as you can not get the oil pan off you could pull off valve cover and see if you can see any signs of leakage where the pushrods come up
if it is a hole in the liner a piston can block it off when not running and hold the water in
thanks for the info it is very helpful...i will let you know what i find