How did you take the 2 pieces on the left apart in your pic? I took my T stat out on my spare housing and those 2 pieces won't separate. It looks like they are held together with a black rubber seal. Those 2 pieces make up the T stat assembly (I think), item 86, and is what you get if you buy a new one from Mercedes, which is what I plan on doing. I'll post pics of mine later.

http://www.peachparts.com/shopforum/...hermostat4.jpg

http://www.mbpartsworld.com/images/p...185.920716.jpg

I would say yes. I'll do that same test with my good one to confirm.

I think it's a Teflon disc but not certain

I just pressed the two parts apart. It's just a snug fit, nothing special.

Why did you press them apart? Is the part of the T stat the non bronze piece (with the 4 vent orifices, you called it a piston) that does the sealing between oil pump and oil cooler? I think it is but need to study it more to be sure.

My stat is marked 03X, not sure what that means and not sure what year or what engine the housing came from. I'll get a p/n off the housing later.

http://i31.photobucket.com/albums/c3...801_121408.jpg

The stem extension is 7.5 mm at 90F ambient which I think = failed.

Edit: I think this T stat and housing may have been messed with. The end cap for the stat (item 83, Mercedes calls it a valve seat) was very loose and required no torque to remove.

http://i31.photobucket.com/albums/c3...801_115948.jpg

What test?

Pouring water...

I've got 4.61mm stem extension on my good thermostat.

I don't think that is a valid test after looking at my stat. Those 4 vent holes will let the water through and will also let oil through to the cooler before the stat opens. So I don't understand the FSM test that says you should get a sudden rise in temp at the inlet of the oil cooler when the oil reaches the opening temp of the stat.

Edit: I mis spoke. Those 4 holes are the path of oil flow to the oil cooler. How are they sealed against the housing when the stat is closed? I'll have to take a closer look at the housing.

Yea, I'm agreeing with you on that.

mach4, do you know if p/n 1171800175 is the 110C T stat?

It's $47.50 from mbpartsworld REGULATOR. ENGINE LUBRICATION; OIL FILTER made by Mercedes Benz. #1171800175

but $37.95 from ecstuning
1171800175 - REGULATOR,OI - ES#1644529

Anyone buy from these outfits before?

I have no clue...

I was running 180F on the trip back from the junk yard today.

Just spoke to ECS. They will check with their Mercedes specialist on Monday if it's the 110 C stat and if it is available from Mercedes. They also have the gaskets. I don't think it is a good idea to put in a used stat considering what can happen if it fails in the wrong position.

Make sure you get the waffle gasket

You want the one on the right...notice the difference in texture and thickness compared to the non-MB one!

http://www.peachparts.com/shopforum/...ne-gasket1.jpg

http://www.peachparts.com/shopforum/...ne-gasket2.jpg

I will thanks.
Have you checked your pressure relief valve? Pushed hard on mine with a stick and it didn't move. Made a tool to get the screw cap off but it's too tight-need to apply more torque to get cap off. Meanwhile took cover off the other ports to look at the pressure relief valve and noticed a rod inside the spring which should not be there per parts diagram. Can you check yours?http://i31.photobucket.com/albums/c3...802_075351.jpg

I tested the pressure relief valve and it works fine. Takes a fair amount of pressure, but that's to be expected given the pressure it's designed to open at. Haven't made a tool to open it up so can't comment on that aspect.