A friend is concerned because his '80s SD had a thermostat malfunction that MAY have resulted in a blown headgasket, cracked head, or cracked block.

My question is, given the robusti-tude of these engines, is any damage other than the gasket likely?

Was it a 617 engine or a newer one with an aluminum head? If the former, probably a gasket. If the latter, probably more serious problems.

__________________
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

I don't know enough about " SD's" to know if that means the 300 only..
Do you know any other things about the episode ... like the temp shown on the guage, how long, and whether any water was added to the system before it had a chance to cool ...?

Hello Jim B+
Year, make, model, please.
What where the exact circumstances and how long was it run at what temp.
Who did the diagnosis, gasser mechanic or good diesel mechanic you know and trust?
Will he attempt DIY repair, independent shop or MB dealer?
Does he have service information?
Will you be helping with advice or hands on?
More data needed for a real usable answer.

The base answer to your question is; anything is possible.

Sorry "Jim", not trying to be sarcastic or rude, just relevant questions and answers.

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

During one of those 4 degree days a few weeks ago, I noticed that I wasn't getting heat and my termp gauge was shooting up! It quickly pegged 120 as I pulled off the road and killed the engine. I was thinking water leak but the water level was fine. After it cooled off, I drove it home without heat.. I changed the t-stat with a new one from Autozone. All's well, heat's back, engines fine. ***** happens in extreme cold with these cars.

__________________
85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)

I'd change the oil and not worry about it, they's tough..........

William Rogers.......