I don't find it odd that the engine had to be removed and tore down with less than 200k miles since it had an improperly setup cooling system.

Thats because customers that take their car to somebody to be repaired rarely keep records of fuel economy and wouldn't notice 2-3mpg less.

"Suggest" all you want, that doesn't make it the correct choice.

Dad insisted on the overhaul at 194,000 miles. There was nothing found to suggest ot needed an overhaul. That's just how Dad is.

My 1978 300SD had the 60°C thermostat in it when I bought it at 224,000 original miles. I put a 60°C back in it, because the dealer offered me both a 60°C and 80°C for the 617.950 by application. I drove it another 87,000 miles running it 'dangerously cold' (as you say) until it rolled up 311,000 miles.

Althoough it was still running quite well, I decided it would be a good time to go through the drivetrain.

Again, when actual results argue with theory, believe the results...Robert

Ok, Ok....You win...

Go to the parts counbter at Mercedes-Benz of Fresno and ask them for a thermostat for a 617.950 engine. When they ask whether or not you want a 60°C or an 85°C, argue with them that it isn't the correct choice...Robert

Thats why they ASK what you want. Geez, can you not get the point after a dozen posts of saying the exact same thing back-n-forth?
Its the same reason why oil change shops ask what type and weight oil the customer wants to use. It doesn't matter what the correct choice is if the customer wants differently.