Anyone have a cracked monovalve in either 300D-2.5 or E300D? (W124)
 

I would like to hear from any E300D (1995) or 300D2.5 (1990-93?) owners who have had problems with a cracked plastic body in the combined monovalve/aux pump (001 830 40 84). The part number is unique to these two models and is very expensive (~$500).

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In early 2013, the monovalve in my '95 E300D started leaking due to a crack in the plastic body. I replaced it with a new one from The Classic Center in Irvine, California. A couple of months later the new one cracked and leaked. It was replaced on warranty by The Classic Center. The replacement lasted another month or so and then it began to leak.

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This is a puzzle. The monovalve is mounted on three flexible rubber stand-offs; there is a minimum of physical stress placed on it. All of the connecting hoses have been replaced as a precaution. The plastic body of the monovalve has no recognizable markings. The metal body of the monovalve is marked "Bosch" but whether they made the entire component or just the electrical parts we do not yet know.

Next, I went to my local dealer, Mercedes-Benz of Santa Rosa, California (MBSR). They were very supportive and ended up replacing the monovalve themselves at no cost to me. This eliminated any errors that I might have made. The third replacement lasted a couple of weeks and then it too cracked. MBSR and I decided there was no point in wasting time replacing the monovalve a fourth time. They have sent a report to Mercedes in Europe in the hope of finding some kind of manufacturing defect.

By accident I discovered MercedesShop member "chronometers" (Chris), who also has a leaking monovalve problem with his 1995 E300D. His monovalves crack and leak in the same place mine do. His first came with the car and the second he bought while on a trip in Germany.

I have been able to minimize the leak by keeping the pressure cap loose on the expansion tank but this is clearly not a fix. To provide additional ammunition to my dealer in their work with MB in Germany, I'd like to hear from other owners of this same part, limited to the 1995 E300D and the 1990-93 (?) 300D-2.5. Have you also had this problem? Have you never had this problem and think we're all crazy? Please let me know!

Jeremy

Jeremy, on my 91 and 92 300D's, the aux pump and monovalve are separate components. Are there some where they're combined?

In EPC, part number 000 830 40 84 comes back to the 1995 E300D and the 300D-2.5 (OM602 Turbo). There's a way in EPC to tell what years they refer to but I keep forgetting how to do it. Maybe it's only the 1993 300D-2.5? Someone should know. Thanks for the word on your '91 and '92.

I suspect that Mercedes used this version of the monovalve for smog control. By having a flow of coolant through the head at all times, whether the heater is being used or not, they can keep the head at a more constant temperature. That should make the smog control tighter. I do not know this, it's just a guess on my part.

Jeremy

Wow. That is one....expensive....part.

Another
 

Mr./Mrs./Ms. ,Owner

You must be mistaken,Yours are the ONLY Mono-Valve composite ingress fitting
that've leaked ...
Too Bad, So Sad!
None of our "anointed" suppliers produce defective parts!
(AND if they did We'd catch them before they got to you!)

Please stop Abusing your Mercedes,else we'll be forced to Excommunicate you
from the Owner's lists.

same here when I bought my car, the car was actually stalled and this piece snapped off at the very same point, I thought this break off was due to someone trying to replace the battery with the hood not fully lifted up. The break off was at the very exact points you have marked. When it was apart, it seemed that the item was heat brazed or melted on after production.

I used the radiator tank repair kit from NAPA (the kind that heats up mad and comes with a fiberglas cloth) after I first cleaned it to surgical level and roughed it up with sand paper all the way inside out.

IT STILL leaks a very slight amount.. But has not blown on me (fingers crossed) causing a very small coolant loss every 5000 miles, Oddly the system holds a very good vacuum and the upper coolant hose is collapsed under vacuum in the morning meaning the cooling system is tight.

I did not bother with a new part as it was 500 dollars something. The turbo 2.5 cars dont have this, Ive looked at about 6 different ones and all have separate items.

Repair or replace?
 

I agree -- two separate plastic parts are fused to create the body (plus the bottom).

I may try that on my original monovalve.

<snip>

Thanks for that. I'll have to re-read EPC; maybe I'm seeing an incorrect reference or something. A part unique to one year and model would certainly explain the exorbitant price.

Jeremy

By the fusing I meant that if you look at the other pipe barb fittings you can see they are part of the mold, when I was repairing mine it seemed that this particular barb was not part of the mold and was tacked on as a separate item. It only has a very thin area where the fitting is fused to the main body.

Looked silly to me. But as mine is functioning good albeit leaking a tiny bit Im not complaining because the new part is 500 greens.

Joint problems
 

I agree, as does everyone who has seen the monovalve, including my dealer. Somebody screwed up with that design.

Jeremy

Break point
 

EPC shows that the 300D-2.5 Turbo (124.128) "up to ident. no. B 926098" has a separate monovalve and pump while "as of ident. no. B 926099" uses the combined valve/pump. Anyone know the break point date? Is the "ident. no." part of the VIN? I suspect that only the very last year, maybe not even the entire year, had the combined valve/pump.

Jeremy

good to know this.

Thanks.

Yes, I believe ident. no. is part of the VIN.

I've just heard from a knowledgeable Mercedes owner that "B92xxxx is a very late 1993 model year, probably May/June 1993 build (approx)." Since 1993 was the last year of the 300D-2.5, that means few were made with the combined aux. pump / monovalve and even fewer remain today.

Jeremy

Sure glad mine don't have that, ahem, "upgraded" part.

The thing that's unique about the monovalve (whether combined with the pump or not) is that it's "SPDT" (if it were an electrical switch). There is always a path for hot coolant from the rear of the head to the thermostat housing. Depending on the position of the monovalve, the coolant goes through or bypasses the heater core but the flow is always there. I assume Mercedes did this for temperature control, to "improve" smogging. In any case, it appears to be unique. Other Mercedes diesels (and some gassers) have no coolant flow from the rear of the head when the heater is off. Weird, huh?

Jeremy

sounds like they wanted to heat the head evenly and to prevent air pockets. Its a pretty high point in the system, It would become nightmarish trying to purge the trapped air if it did not have such a setup.

Good point. I think that's why the instructions for filling the cooling system always say to park the car nose uphill if at all possible and run the car with the heater in Defrost (forces full heat).

Jeremy

Nick Stauer of MBSR made it right!
 

To follow up to the earlier posts, Mercedes has reimbursed me for the $500 I spent (back in January 2013!) on the first (of three) replacement monovalves (all of which cracked and leaked). This reimbursement happened when the local service manager, Nick Stauer, of Mercedes-Benz Santa Rosa (California), spoke to the new factory rep for our area. She agreed to put in a request for a "reimbursement for leaking monovalve" (their words) and it was honored. I got the check yesterday.

This was on top of replacing the monovalve once themselves at no cost to me. Their replacement lasted less than a month but it confirmed I wasn't doing anything wrong when I did the work. So their actions are definitely above and beyond what one expects from car dealerships. I am pleased. All hail Nick Stauer and Mercedez-Benz of Santa Rosa (aka Smothers European).

That it took three years is unfortunate (better for them if I had sold the car or died or moved away). Once I had patched the original monovalve (stopping the leak) the pressure was off and I didn't push as hard as I might have done.

It also suggests that the factory has no intention of getting their subcontractor to build a new, non-cracking part. This I expected from the beginning; why go to a lot of work to re-design a one-off component used in 3,000 cars 20 years ago? BTW, a new monovalve/pump (001-830-40-84) is now $900 or so I've been told. Caveat emptor!