Put a lower radiator hose heater in instead. It's not worth the headache to try to get the plug out. As I recall, an 1 3/8" heater works. DieselGiant sells heater with the hose already attached or you can buy the heater and cut your hose. Takes half an hour to install with no risk of cracking the block or your knuckles.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13