How fast were you driving at 4500rpm's??

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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

+1, I'd like to know too...that'd be pretty much WOT in my wagon which'll heat things up a bit though I wouldn't go as far as saying its the cause of the overheating. Certainly couldn't help.

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)

I'd place my bet on the radiator. If its over say 10 years old, just replace it. I also saw a thermostat problem that caused overheating. even a new thermostat is to be suspect. A sticking thermostat will mimic a bad cooling system.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

If the thermostat is malfunctioning, the cooling system is bad.