Tractor Repair: tractor radiator in a 6300 john deere, sludge, radiator

Question
i put anti freeze in the radiator before xmas and one day i checked as i always do for water level and i found a gunk like liquid just at the filling point,i was tols by a neighbour not to panic that it was the anti freeze that had done it wen the hard frost was around,would this be right

he give me radiator flush but the only trouble i have now is i cant find were the draining bung is in the radiator

Answer
just take the bottom pipe off the rad to drain it. if you put enough antifreeze in it couldn't freeze what color is the gunk? most likely oil residue from a oil jug used to fill the rad but you could have more problems but you are on the wright track use the rad flush as described on the can i normally put two cans into tractors when that is done refill with water and work the tractor for a few hours and see if the sludge returns if it does you could have a burst engine oil cooler or cracked block.how did you notice the problem was the rad blowing off or were you just checking the water level?