Mabe the last person who worked on this couldn't get the thermostat out, used a long screw driver to pry it out, and broke it? Not having a replacement, decided to put it back in?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I always attributed it to the extreme heating and cooling for 30 years. IIrc mine didn't have much corrosion on them at all but took very little to snap off.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Heating and cooling? These are not exhaust bolts. All bolts on the engine go through heating and cooling cycles. Did Mercedes use substandard bolts on the T stat housing?

I had the T stat housing off both my 83 and 85 recently. The 83 came off easy because I used anti seize last time I had it off (approx 4 years ago). The 85 I bought recently was very tight but I used penetrating oil and the palm impact on the 1/2 drive ratchet and they cam off without breaking. One of them was very tight after cracking and I used more penetrating oil and back and forth with the wrench.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Beats me, but it almost seems like it. They're the only bolts (aside from exhaust) on the whole car that have ever snapped on me. I distinctly remember them appearing clean because I couldn't figure out how in the hell they got so weak.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

It's fatigue from the spring tension. I have seen a number of thermostats with similar failures.

I need to ask the owner to check his records, but he's always had the car maintained at a fairly reputable shop. Id assume that whoever busts the thermostat like that would have the sense just to remove it completely until they got another one instead of reinstalling a restriction on the cooling system.

more likely it was just fatigue though, as qwerty says. I didn't see any scuff or pry marks on it.

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Fatigue could explain it, though I've never had one which broke like that. I've had one stuck slightly open resulting in a cool running engine. So you were just unlucky and it broke on you while you were hundreds of miles away from home? Did it break in a stuck open or stuck shut mode?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

basically the short answer is I should have known better than to take this car any distance without resolving this problem, as it was known by me that it ran hot if you drove it over 15 minutes.

The owner says it always ran about 100c for at least the last 6 months, or just above, and it started to spike under load halfway down to the GTG.

Im assuming that it was jammed in there blocking flow, but not completely, since the car never truly overheated unless you really put a load on it past cruising.

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Sounds like you could have drove it slower, under less of a load and made it back?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

now that I think about it, actually it was traffic that did it in, not speed. Airless heavy traffic in NYC temp started to rise, not enough airflow. Would also start to overheat when you crept past 65mph

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How bad did it overheat? Did it vent coolant?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

nope, just spiked a couple times to 120, and after that, would get that hot quickly even after letting it cool down, so I figured the thermostat was just jammed well and good.

had it towed from there, im not playing around with overheating a car thats not my own.

I might have tried to limp back in my own car, but not a friends car (that I would have to fix or replace), plus I have a AAA elite membership, so it came under the 100 miles of free towing a year.

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Did you consider going to a movie, then go out to dinner, after the evening rush hour when it's cooler with less traffic then drive back?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I am going to bet that dropnosky conducted a detailed and extensive cost/benefit analysis that led him to conclude that it would be a lot easier to get AAA to pay for a tow than it would be to get them to pay for a dinner and a movie.

Did you consider that?

lol, I wanted to get home in some kind of reasonable time, I was 188 miles from home. Had it immediately towed to a friends house in southern ct, then subsequently broke the bolts, at which point hopped on a train and went home.

Even still, resolving the three bolts with this car took the entire weekend of mostly travel, about 1/2 hour of actual repair, to the extreme displeasure of the girlfriend. Had I seen a movie on top of running all over CT, I probably would have been slapped.

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