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Mono Valve Sources

9K views 15 replies 8 participants last post by  manabenz 
#1 ·
Hello all. As anyone that has had a w123 (and also I believe w108/w109), the Mono Valve is a major issue when it comes to getting heat to work. The main failure point is the rubber diaphragm. When it tears, water gets behind it, and closes it. Therefore, you get no heat at higher RPM's, or even no heat at all if the tear is big enough. The only source for replacement parts seems to be Mercedes, BMW, MTC, or VOLLIG. BMW price is right about $150, Mercedes is about $210, MTC and VOLLIG is around 20.

Bosch used to make a part, but it is NLA as of around 2010, but I belive they make Mercedes and BMW's part in France.

I wonder if anyone has had success in finding a Bosch source, either NOS, or out of France where they are making OEM's parts. I have had a few MTC parts, and am going to give VOLLIG a try, as my MTC part has failed yet again.

I am also interested if anyone has repaired the rubber diaphragm successfully for any length of time, and what your experience has been with any of the mentioned brands.

Cheers.
 
#6 ·
W124 Monovalve in W123

Here's some pictures of what I did. The original valve was removed and I used a length of heater hose to replace it. Then I removed the auxiliary pump and being a little creative with an 90 degree ebow and piece of orginal hose from the 300E, installed the new valve in it's place. The rubber holder for the pump worked good to hold the new valve in place, I just used a piece of hose cut lengthwise to make it a little more snug. Used genuine Mercedes connectors to lengthen the electrical lead to the valve.

The W124 monovalve (part no. 000 830 72 84) is an improvement over the W123 design. There is no rubber diaphragm and the plunger moves against the flow of coolant instead of with the flow, to close. So there is no diaphragm to tear and the plunger will not be sucked into the closed position at high engine rpm's. The basic concept is the same in both valves. It seems to work just fine. I lose a bit of heating capacity at idle without the pump, but older pumps can draw more current and cause a false closure of the valve resulting in no heat at all. Since the pump was disconnected anyways, that is why I installed the valve in that location. I may try to refurbish my pump and re-install it, but the new valve will stay. Unless I checkout the BMW part. I saved all my old parts, so I can retrofit if I decide to do so. BTW, what year/model BMW's would that part be used in?
 

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#7 ·
Here's some pictures of what I did. The original valve was removed and I used a length of heater hose to replace it. Then I removed the auxiliary pump and being a little creative with an 90 degree ebow and piece of orginal hose from the 300E, installed the new valve in it's place. The rubber holder for the pump worked good to hold the new valve in place, I just used a piece of hose cut lengthwise to make it a little more snug. Used genuine Mercedes connectors to lengthen the electrical lead to the valve.

The W124 monovalve (part no. 000 830 72 84) is an improvement over the W123 design. There is no rubber diaphragm and the plunger moves against the flow of coolant instead of with the flow, to close. So there is no diaphragm to tear and the plunger will not be sucked into the closed position at high engine rpm's. The basic concept is the same in both valves. It seems to work just fine. I lose a bit of heating capacity at idle without the pump, but older pumps can draw more current and cause a false closure of the valve resulting in no heat at all. Since the pump was disconnected anyways, that is why I installed the valve in that location. I may try to refurbish my pump and re-install it, but the new valve will stay. Unless I checkout the BMW part. I saved all my old parts, so I can retrofit if I decide to do so. BTW, what year/model BMW's would that part be used in?
Thanks for the photos. Does that w124 assembly have the same electrical control? I think with enough finessing, you could probably put it in the original place on the bulkhead, and keep the aux pump and original wiring.

The part number 64118390132 for BMW is the rebuild kit, just the same as the MTC/MB one, but cheaper. It looks like they used an almost identical system from 78-89, in their 5, 6 and 7 series.

EDIT: I also commend you on using german style hose clamps that don't dig into the rubber like the US ones. ;)
 
#8 · (Edited)
The coil in the two valves appears to be about the same, although I didn't test the resistance or anything. It works the same; energized is closed. The valve is meant to be mounted vertically, but for on/off operation it works horizontally. Yes, I used original Mercedes hose clamps for a more original look.
 
#9 ·
I am going to try to get my hands on one of the w124 mono valve (000 830 72 84) and see if I can build a mount for the original location and manufacture some kits for people with this same issue. Will be an interesting project. Thanks for sharing your solution!
 
#11 ·
Many enthusiasts have mentioned buying the MTC and swapping the rubber bits to the original mono-valve. The big rubber diaphram is what splits and leaks, everything else is just metal.
 
#15 ·
The cheap one has the rubber galvanized in 4 small spots around the top of the outer ring of the metal spring holder. Gently slide a very small screwdriver under the rubber and you can gently, gently, gently pop the rubber away from the metal. Then swap the e-clip and you are in business. The OEM metal part where the rubber mates appears to be slightly smaller diameter. I have not verified this with my micrometer but I got a perfect fit.

I have done this and with my MB stem and cheap rubber I am in business. I did also buy a $49 MB spare.

Good luck!

Kyle
 
#14 ·
The Mercedes part dropped from $260 down to below $50 a couple of months ago. We were talking about this at length over on the W126 forum. I verified the price with my dealer and a couple people actually bought some from their dealers at the sub-$50 price. In the last week or two the price shot back up to $260.

I'm going to be at my dealer today and will quiz my 20+ year parts guy as to what's up, as he had checked and verified the price for me when it dropped to below $50.

I've seen some parts price swings in my day, but nothing like this.

Dan
 
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