I was just gonna ask the same question.

Unless you really fried it (ran it til it locked up), a blown head gasket normally requires only a new one to fix the problem.

Severe overheating will crack or warp the head (so badly you can see it with the naked eye), and will destroy the pistons and cylinder walls. Very unlikely to do even that if you shut it off right away.

I guess significant amounts of coolant in the oil would do some damage, too, though....

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!