One of the forum members was kind enough to send me a used monovalve element for cheap. As I've never replaced one, I want to make sure I know EXACTLY what to do and what, if anything, to look out for.

I found this: http://www.peachparts.com/shopforum/showthread.php?t=135721

So I assume I:

1. Do this when engine is cold.

2. Remove four screws that hold cylinder at top of monovalve.

3. Swap out the valve element.

4. Put cylinder back in place.

Is that all there is to it?

Also, will I lose much coolant? I lost more than I should have recently when I replaced my aux water pump and thus want to avoid any dumb mistakes.

Finally, why do people replace the entire monovalve? Are there other components that typically fail?

Thanks!

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

that's it.
however, before you put the new kit in, look in your old body, and clean out any gunk that is in there. also, if it is corroded inside, remove the entire valve from the car, and clean it with a wire brush first. look out for cracks and pitting. if the thing is in bad shape, a new kit will not help.
other things that fail are the CCU, if it's got a bad aux pump on it, the ccu may be burned. if it's burned, the monovalve won't fix the problems.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

By "other components," I meant things within the monovalve itself. But it sounds like, other than dirt/corrosion, that one part (either because the rubber tears or it won't move) is all that can go bad.

Will any coolant start coming out when I open it up?

__________________
14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

You should not lose any coolant. Maybe a dribble. But, not enough to worry about.

Be sure the washers go back in the proper order.

__________________
AJ

1985 300D (SOLD)

bbbbbThe 124 chassis monovalve assembly is different from the 126 and 123 valves for which there is a replaceable plunger/diaphragm repair kit available separately. Before you open up your monovalve you might want to do some research if anyone has repaired a 124 monovalve using a replacement plunger/diaphragm, you might be able to successfully cannibalize another 124 valve for a good part, but I would be concerned that the 123/126 repair part may not be an exact replacement for the plunger/diaphragm original to the 124 monovalve, and if you've got things apart and it doesn't fit correctly you could be screwed if it doesn't go back together and seal up correctly.

FastLane only lists a complete monovalve assembly and the EPC does not show the plunger/diaphragm as a separate part either.

I'm pretty sure that's what I have. I didn't get a repair kit, but rather got a cannibalized part from another forum member. I'm taking his word for it that it's the exact part.

Right now, heat is good. But as I have two virtually identical cars, I notice the smallest differences. The heat on the 92 is unbelievably strong....it had the complete monovalve assembly replaced last year when heat was noticeably anemic. On the 91, it definitely blows hot (as opposed to warm), but it's not as hot as the 92. So I'm suspecting a worn monovalve. But I'm sure I'll live with it until it gets more noticeable.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

If the source of the part specified that it came from a 124 monovalve that would be a differnt matter, there is a person offering inexpensive scavanged plunger/diaphrams from 123/126 vehicles that may not be the same as the 124 part was my caution before you get things apart and find out things are incompatable!

Any hints on what that order is? When I pulled my old one, the circular spring was disintegrated so I can't put it back the way it was, I don't know what "was" was.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

If there is an issue with the valve you are hoping to install, I have a valve from an 89 300 if needed. Just drop me an email.

note: you lost coolant swapping the electric water pump, because of how low it is in the system. Components at the top of the cooling system, rarely cause fluid loss when disconnected for service. You wont lose much.

FYI. That valve is in a pain in the butt spot. You may have to pull the battery to make life easier. If you've done this already (as per your posts) then you should already know how much coolant to expect to lose.

Best of luck.

__________________
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.