1. Is it a genuine Bosch, or a just a MTC monovalve?

First, how can you tell just by looking at a repair kit if is a genuine Bosch part, or an aftermarket replica in a Bosch box? What if you find an EBay repair kit, and the seller says is a Bosch? Is any way you can verify is not a MTC? It turns out that the used parts I have (old monovalves with broken diaphragms pulled from MBs) and the new Bosch, they all have (w/o exception) something in common: on the side of the rubber diaphragm I found the raised letters: MB 30-28. The MTC did NOT have that, also the BMW did not have it. Furthermore, the MTC spool does not appear to have the brass wire mesh that the Bosch has, also the circlip on the brass rod does not appear to be made out of brass on the MTC model, see below picture (John mentioned the non-brass circlip too in his post). Based on the above, I concluded with a high level of confidence that the Bosch kit I purchased from Napa is actually the same part that MB used.

 

Do they have the same dimensions???

Well, first let’s measure the OD on each kit, as they come out of the box. Below are the dimensions: MTC, Bosch and BMW. Notice that MTC is bigger by almost 1mm. That will cause a problem, shown in few moments. Also please notice that the MTC does not have the brass circlip.

 

Let’s build the “hybrid”

As John described in his thread, the monovalve body, circlip and spacer can be used with the MTC spool in order to obtain a fully functional unit. From this point forward I will refer to this new part as being the “hybrid”, because is not entirely a MB, but is not entirely a MTC either. Below are the two pictures showing:
- First picture: the MB (used) parts to be re-used (upper) and a MTC monovalve I was just a bout to take apart (lower),
- Second picture: what is left of the MTC kit (upper) and the new “hybrid” ready to go in the heater valve body (lower).

 

How good of a “drop-in” replacement will the hybrid become?

Well, that’s where the fun part starts, and one of the purposes of this thread… Measuring the OD of the hybrid, we still get more than 30mm. The monovalve seat in which the diaphragm will install has an ID (Internal Diameter) of 30mm (red arrows pointing). At this point forward expect that issues may occur with the hybrid because its OD is greater than the seat’s ID which means you may have trouble seating it right in the heater valve.

 

How does each of them fit?

Below please see (in order) the Bosch, the BMW, and the MTC. As expected, the MTC does not offer an easy fitment because of enlarged diameter that does not allow the monovalve to seat properly in the corresponding seat of the housing. The Bosch and the BMW had no problems in that respect. If the MTC is forced w/o having its diaphragm helped to fit correctly (task that tested my patience and took me two years ago about 15 minutes), it will be forced to roll its edge in order to fit into its housing seat when the monovalve is pressed down, it will still seal against the coolant, but the rubber will be stretched and stressed, which in turn will contribute to premature rupture of the diaphragm (on top of the fact that its rubber does not appear to be high quality to begin with).

 

Are there other differences between the hybrid, Bosch, and BMW???

Well, actually there are:
- The rubber diaphragm acts like a bellow. From the first picture below (from L to R: Hybrid, Bosch, and BMW) you can see that the BMW has “more bellow” than the other two. Is also my opinion that the quality of the rubber is a bit better on the BMW than on the Bosch
- The MTC rubber diaphragm also looks a bit cheaper than the other two. In fact even the injection mold was a cheap part, not meant to generate too much quality to begin with. Note please the circle marks (the round circles on the diaphragm’s surface) which are nothing else but tooling marks from the mold manufacturing process. Such marks are not present on the Bosch or the BMW diaphragm.
- My biggest surprise (initially I assumed that the Bosch and BMW are actually the same Bosch part) came when I looked under the diaphragm: the BMW has an extra rubber washer that the Bosch does NOT have (green arrows pointing). That extra part has the purpose of reducing the stress that the brass washer would put on the diaphragm and the direct contact between the two parts. In addition, without being an expert in rubber parts by any stretch of imagination, is my opinion that the BMW diaphragm is a bit thicker and the rubber used appear to be a better quality than the Bosch.

 

In conclusion …

1. There are ways to correctly identify the MTC, Bosch and BMW monovalves.
2. The MTC is a lower cost replacement, and its quality is reflected by the price. I don’t expect great life out of it, is not made to last. The parts that were not used in building the hybrid appear also low quality by comparison with the similar MB used parts. The only surprise I had was that the spring of the MTC appeared to be a strong one, maybe even a bit stronger than the Bosch. John saw exactly the opposite, so don’t throw away the MTC until you make sure the hybrid works fine.
3. If the MTC is your only option, when you install it make sure you will fit the diaphragm correctly in its seat. Do not put back the rest of the parts until you are sure it seats correctly into its seat.
4. The Bosch (if you can still find it) is good quality at a decent price, it appears to be exactly what MB used.
5. The BMW part does not appear to have the same components as the Bosch, and I am under the impression that either the BMW is made by Bosch under specific BMW standards, or is made by someone else, perhaps even BMW.
6. The BMW appears to have the best quality overall and a bit better design. In my opinion it would be the best choice for a long lasting solution, but unfortunately I cannot advise how it would perform (my car will not run for at least one more year). If you can afford spending the money, this appears to be the most reliable solution. It would be nice if a member will use it and share with us his impressions.

Thank you for reading.

 

I have the duo set-up in both my coupes with the dual cabin control temp wheels for left ad right side.
It would be handy to know who can supply the repair kits for the Duo Valves?

 

Nicely done Roy. Thanks for taking the time and making the investment to help with this perennial problem.

 

I am glad I could help. Reading it all means you did not fall asleep reading.:grin

Actually John should get some credit too, I did not think of it until I saw his post.

I decided to make the investment after I noticed that the Bosch is NLA, not even at Napa. I was afraid the same may happen with the BMW monovalve, so I bought myself one. Our brothers from BMW are using them too, so its future availability may be uncertain.

 

The DIY post has been updated.

http://www.benzworld.org/forums/w12...s-se-sec-sel-sd/1340751-do-yourself-diy-repair-thread-wheel-9.html#post13253049

 

Good writeup!

The duovalve uses two monovalve kits (go figure...)

Interesting about the difference in OD. I did not take any special care when installing my "hybrid" valve kit. That said, I doubt I got it in correctly, although it continues to work... (Antifreeze is very slippery...)

Did you actually measure the spring tension? What did you get? I'm very surprised you found the MTC to be as strong as (or stronger than) the Bosch valve. My MTC kit is (was) over 1 year old, so maybe they got the message?

 

Thank you, John.

If it does not fit correctly but is installed w/o noticing, it will still work and seal, but the diaphragm will be already stretched a bit on one side. That will shorten the life of the diaphragm because when the spool will move it will stretch it even more. Eventually it will break from the side that was already stretched.

I did not measure the spring tension with a device, only what I could tell from me pulling the spool. It surprised me too. However, my impression is that the MTC box is older than 1 year, and has different graphics (higher price too) than the other MTC I bought two years ago and I installed in the car. Maybe I have a softer spring because of a Bosch defect, if indeed my "fingers gauge" were correct?

MTC (Mission Trading Company) is not a manufacturer, is a wholesale auto parts supplier, so is very possible that the part I have may be from a different MTC supplier than the one you have. Judging by the box, I would say that what I put in the car two years ago is worse quality than the one that I got now.

 

Box? I didn't get a box...

 

The white box is for the kit I bought 9/2013 for $15. The other box (bigger)is what I bought recently from EBay, a private seller of BMW parts, and somebody wrote on it 2/12 and $ 79.95.

Is possible that you got something very poor quality, if it was very cheap. I mentioned earlier in the thread that there are different degrees of quality for the same MTC part.

 

I can attest to this info as Roy educated me with those valves just the other day. It was something I didn't pay attention to when I changed the monovalve in the SE a while back, IIRC it did fit just fine and no I can't remember it's brand

 

It was something I didn't pay attention to when I changed the monovalve in the SE a while back, IIRC it did fit just fine

Is not easy to see if it fits or not, you'd have to look inside all around the diaphragm after you place it in the heater valve body to see if it seats right from the very beginning (have a flash light ready). Most people don't do that because they would not expect a problem there (I confess I did not expect that either), and is also not easy to see inside. As I mentioned already, if you add the rest of the parts (washers, spring washer, coil, retaining plate and the screws) it will still seal and work, but as is pressed into the seat by the rest of the parts, the diaphragm will be stressed and would fail sooner.

The best way is to measure the OD of the rubber diaphragm just before installing it: if it comes out to (let's say?) more than 29.85 mm (approximately 1.175"), expect to add extra work in making it sit correctly.

I would be curious to hear the opinion of somebody else who will change it, and find out what the OD was before installing it and if he observed the same fitment issue during replacement. The OD was greater than 30mm on the MTC repair kit as it came out of the box (on two separate MTC kits), and also on the hybrid I built.

 

We can't one just retrofit a heater valve from a 300D, which seems to be different, or even a newer Benz with the push-pull solenoid? This way we could simply avoid the obsolescence factor.

 

The original BMW kit and Mercedes kit were the same, so the present day replacements should be compatible. I doubt there is a peculiarity of the BMW (or MB) installation that would make it otherwise. (Both even use an auxiliary water pump.) I have a BMW part on order. I was intending to hold on to it until I needed it, but maybe I'll give it a try sooner.

OBTW, my old part, which is either original or a very old replacement, has the "MB30-28" (or whatever it was) lettering on the edge.

 

I'm looking into it now. I'm not certain why it is not working.

--Kyle

 

I'm working on it, I'm sure you guys don't see the value in receiving emails that may not pertain to your chassis or make. This thread is about the Monovalve and I don't want to stray too far off the topic so it's the last you'll hear me bring up emails.

--Kyle

 

Gentlemen,
Could any of you lay out the coolant flow path through monovalve? There are three openings/tubes going to the MV, one from the auxiliary pump one to the core and one a bypass to the water pump, am I correct so far? What I am trying to figure out is flow paths in different settings i.e. fully MV closed, and control set at say 75F (Partially open).
I am trying to understand why I lose heat around 2000 rpm or highway speed. I have been led to believe that the culprit is the MV spring tension and unequal pressure across the rubber bellow.
Thanks

 

The flow enters at the top (two hoses coming from the heater core) and exist at the bottom (one hose towards the auxiliary pump, on some models also a smaller hose for windshield and its fluid heating). Below is part of the text in my PM to Ken D that addresses this issue. One thing that perhaps I should have insisted a bit below, is that when the valve is open and the coolant travels, it moves in the space left between the plunger and the valve's walls. Unfortunately, there is only so much fluid that can "squeeze" around the plunger and the valve's wall, so some residual pressure appears in that section. Well, the more flow passes, the higher the pressure upstream is, and at some point the flow "takes with him' the plunger because the spring is overcome (for lack of better words in my description).

'First let me say that there are two rubber parts on the MTC and Bosch monovalve: the diaphragm and the plunger (which is the part that actually closes the flow, is shaped like a cone). Secondly, there is a small hole in the parts sealing the diaphragm with the purpose of allowing a certain amount of fluid to go from one side of the diaphragm to the other as the plunger and the diaphragm will move.

Coming back to your question, I am suspecting that the return spring of the monovalve you have is not strong enough to keep the plunger up. When the vale is de-energized, the plunger will raise (being pulled up by the return spring, and held in the up position ONLY by the spring) and the coolant will flow thru the heater valve, providing you heat inside the car. So, the only thing opening the valve is the spring that pulls the plunger up, thus opening the passage. Now if you look closer at the inside design, you will see that the flow of coolant thru the heater valve housing will flow going around the plunger, but at the same time will also have the tendency to push the plunger down a bit (in the direction of the flow). The faster the coolant flow is, the more will push down the plunger. I am suspecting that your spring (by itself only) is able to keep the valve open (the plunger up) only up to 2000-2500 RPM, over that mark the flow is so big and is pushing down even more on the plunger that the spring cannot hold the plunger up, and the plunger is pushed down by the coolant flow (which in turn means no heat in your car). My opinion is that you need a stronger spring. Unfortunately changing the spring is not an easy job, if doable at all. Moving some parts from the old MB monovalve to a MTC kit is another solution. John explained that very well in his thread http://www.benzworld.org/forums/w126...ning-life.html. Another potential solution is to buy the BMW monovalve kit, provided that is still available, but unfortunately I haven't tested yet, so I can't offer my prospective on its functionality on MB.'

I hope that helps.

 

Thanks, so if the downward flow of coolant around the cone towards the auxiliary pump creat a pressure differential that at some point overcomes the spring tension and closes the valve (Stops flow), once the flow is stopped the pressure diff should go away and the valve should open or oscillate allowing intermittent flow which should provide some heat, may be. Also I felt the spring tension on the newly purchased MTC and compared to my old one out of the car which I have put back in (Will take out again to see if MB or Bosch) and the MTC seems stronger.
Thanks again
Ken

 

once the flow is stopped the pressure diff should go away and the valve should open

Unfortunately that is not correct. Once the plunger closed the valve, the pressure downstream is 0, the pressure above the plunger is even higher. For that reason the differential is actually increased, and once the valve closed the force to open it will have to be greater than before (unless the flow decreases).

Another way to understand it (perhaps better than my explanation): fill up your bath tub with water. Take the drain plug off, and put your palm about 2 inches above the drain hole. You will feel your palm attracted to the hole because of the flow. As you lower your palm closer to the hole, you will feel that force increasing. Now put your palm above the hole, obstructing the flow. Will the force needed to take your palm away be greater than before, or lower? I think this description will answer what happens when the plunger obstructs the flow completely.

 

Bosch and MB are the same. BMW is different as is MTC. I measured the springs in the original valve (Bosch) and the MTC from a year ago and the (presumed) 25 year old Bosch was about 50% stronger.

 

Correct! (Or, not correct?) Liviu165 is correct.

Usually, if you let the engine speed drop to idle the valve will reopen and the heat will work until the next time it gets forced shut.

Something that often (not always) works is to put the temp control on max. The valve never gets a close signal and will stay open regardless of engine speed.

If the valve starts to close the water flow through the remaining opening accelerates. Faster flow means lower pressure below the valve (Bernoulli's principle). As soon as that lower pressure exceeds the spring's force the valve shuts and stays that way until the pressure above diminishes enough for the spring to reopen the valve.

 

I added a rubber disc behind the diaphragm, slightly smaller in diameter, essentially increasing the diaphragm stiffness, now everything works fine no heat loss at any speed.
Ken

 

Great, I am glad to hear that you found a solution. Would you please be kind and post some pictures and explain what exactly that extra piece is, where you got it from, and how you installed it? What you did could help other members here or produce new ideas on how to solve the problem. Others had the exact same problem you had, maybe at different RPMs.

 

Not sure why someone felt the need to report this thread?
Its a bit early for heavy duty eggnog.

Reported Posts vs PM
The 'Report Post' function should be reserved for the most egregious offenses imo. I recall a nasty pic porn thread from Thailand.
Clicking 'report post' is like pulling the fire alarm or pushing all door bells of a high rise, as it goes through all time zones to everyone moderating the forum, incl HQ in Toronto.

In the old days, much of what is being 'reported now' was handled by pm to the forum moderators.
For the little stuff and real or imagined slights / insults, members who like to play grammar police or at moderating without being actual moderators, please PM the specific forum mods.

 

I, too, received the reported posts message but did not see anything that would warrant reporting.