grey black sludge in my radiator???

that's usually an indication that there is oil in the cooling system. Check your trans oil, sometimes when the oil cooler in the radiator fails it'll allow cross contamination. Also check your engine oil, closely check under the filler cap is there sludge milkshake lookin crap under there? That could possibly be cross contamination within the crankcase head, head gasket something along those lines. Good Luck