Well last month, while changing the thermostat on my Euro 300TD, I discovered some significant pitting at the mating surfaces of the thermostat housing that the special giant thermostat O-ring gasket couldn't cope with, so I had to fix it with some RTV.

Happy Motoring, Mark

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DrDKW

That's a good thing to keep in mind. PO had green stuff in the system, and there was a bit of pitting on the T-stat housing. Not enough to cause a problem, luckily (I know the T-stat seal is holding now)...but good to know if I come across something worse one day.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

If I were you, I'd run some fresh water through the engine block when you get the pump out. The 240D I did had some nasty crud coming out of the block after all that time....

-GH

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For Now:
1992 Mercedes Benz 500SL
1998 BMW 528i
2003 Honda Element
2002 CBR600F4i
1977 Coachmen Motor Home

whew - finally got this done. In the meantime I had to deal with a computer problem ... My power adapter burned up, and whenthe repair shop returned the computer to me, they had done me the favor of formatting my hard drive and giving me the latest version of their operating system. grrr.


Anyway, I did use selant on the water pump housing gasket - there seemed to be no way to keep the gasket in place while reinstalling it. I used non hardening gasket sealant on both sides. I did not use sealant on the water pump gasket. So far I have let the car run to operating temp with water in it. Tomorrow I will drain and put in the Zerex/water and ope it holds. So far so good!

By the third time I had to take it all apart, I was pretty fast - I see now how it could be a 2 hour job for someone who does it all the time, but it took me quite a lot longer than that Even the last time (housing gasket wasn't seated without the sealant), from start to finish, it took me 4-5 hours.

Getting that fan back on is a b@#ch!

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

I have done this job several times and I use a LITTLE bit of sealant. They actually make a special sealant for water pumps and coolant systems that resist breaking down.

Yeah Mercedes may recomend installing everything dry and all, but after a few years, they all leak oil and turn your driveway into a dalmation.

Also, if you bought your car used and its been through several owners, they have have used a razor blade, sand paper, screwdriver, etc. and the surface is nowhere near perfect. When your assembling BRAND NEW parts, you can get away with installing it dry, but after some owners been through it, its iffy...

There's actually no paper gasket for my diesels thermostat housing. Just the special rubber ring. I had to do the 300TD theremostat cover a second time, adding sealant because coolant was seeping past the rubber ring due to corrosion of the housing and cover. Ultra-black or ultra-grey RTV works well in moderation, and doesn't look as obvious as the blue stuff. If using sealant for non-coolant related repairs on gas engines with oxygen sensors, be sure to look for 'sensor safe' on the label.

Happy Motoring, Mark

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DrDKW

That's what i ended up using. I chose the non hardening type that is specifically resistant to antifreeze. I figured the non hardening type would be easier to get off if (when) I need to.


Mark, I replaced the thermostat seal, too. I got the part for $2 at Advance Auto. They had to overnight it from another store. I did not use sealant on that seal....

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Yes, there is. You will find it when your bypass hose starts to leak!!!

I was referring to the gasket involved in changing the thermostat. Not the one between the housing and engine block. A paper one I could make myself.

I've been afflicted by 'Murphy's Law' on both of my diesel thermostats.
Previously, when changing the thermostat on my 240D, I bought the parts BEFORE dissassembly, only to find the parts store sold me a generic 'O' ring, instead of the special mutant rubber seal that's required. By Sunday morning, when I discovered this, that parts store was closed. And of course none of the local 'McParts' stores that are open Sunday had such a special seal in stock!

So naturally, when I changed the 300TD thermostat, I made sure I got the correct special seal, only to then develop seepage at the pitted aluminum mating surfaces, requiring a redo with some added RTV. In the dark, by droplight, with the ALS plumbing in the way, on the Friday night before I was to drive the wagon to Kevin's April Mercedes GTG.

At least none of the tiny cover bolts snapped off during my two thermostat ordeals!

Happy Motoring, Mark

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DrDKW