300SEL: Why can't I get the thermostat out?
 

Why, why, oh why? I've got the top half of the housing out, and the t-stat won't lift out. I can spin it, but it won't move upward at all. I've pried on it a bit, but I don't want to trash it. What's going on?

And the answer is... (drum roll)
 

Because you have to pry out the black o-ring first. I was trying to avoid that in case the t-stat was still good, not wanting to damage it. Dug it out with a pick and the t-stat came right out.

By the way, the boil in water test showed no movement whatsoever. I noticed that there are loose rattly bits inside the t-stat. Is that a sure sign of a bad one?

Mine was seized in even after removing the brittle black O-ring out. But I was going in knowing I was replacing it. I picked at it but then just got a vice grip and pulled it out...being careful not to damage the housing that the t-stat sat in. It was a lot more eblow grease than I thought.

Turns out my t-stat was bad (the boiling water test having borne this out), see this thread for details:

http://www.peachparts.com/shopforum/tech-help/352371-yet-another-300se-300sel-m103-overheating-coolant-change-thread.html#post3301916