bet the alternator seized and shredded the belt. Hopefully the engine was not severely overheated and seized...

My 1987 300d went from 85C to 115C in the blink of an eye when my alternator shredded the belt. I got it shut off fast, though and she's still kicking.

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.