grey black sludge in my radiator???

You have a couple of possiblities then

Atf= you need a radiator

engine oil= cracked block, cracked head, or blown head gasket

If you have access to an engine leakdown tester you could pressurize the cylinders with the radiator full of coolant and look for air bubbles in the radiator. Or if you have a cooling system pressure tester you could pressurize the radiator with the spark plugs out and listen for air escaping into the cylinder. A compression test would also give some information.