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C250 Diesel shut-off valve leak repair

95K views 50 replies 25 participants last post by  PlaneCrazy 
#1 ·
I am a lurker. First post.

Due to a few threads on this forum I was able to work my way through several problems on my 1995 C250 Diesel (non-turbo), with a 605 engine (295000kms if you're interested).

After these successes I have decided to describe my fix and post some pics, as it would have made my repair much easier if I could see the part and understand how to take it apart.

There was a major leak on the transparent fuel lines running from the filter - pump - shut-off valve(the black box on the side of the injector pump) - filter - injectors. It looked like diesel was streaming from the underside of the shut-off valve. Also the car was having a very hard time starting first time in the morning, and then would be OK-ish for the rest of the day. Until parked for 8-12 hours it would be hard to start again.

After searching through the forums and reading loads of posts, I got all the seals from the Merc dealer(8X part # MA601 997 03 45) and took all the pipes off, but did not remove the shut-off valve as I was unaware of the seal going behind the valve. Also broke one transparent pipe in the process but got a new one from my Merc dealer for ZAR180 (US$25).

Replacing the seals did not help. In fact, when I looked at the old seals I thought to myself that these seals are in pretty good nick. Luckily somebody who owned the car before me installed a priming pump (probably the person who replaced these seals previously, I've only had the car for 1 year). So while I was priming the fuel line it was squirting out from below the shut-off valve again like crazy.

Took it all apart again and this time also removed the shut-off valve from the side of the injector pump, and replaced the seal behind the pump. (seal part # MA021 997 75 48)

After assembling everything again and priming it, diesel was squirting out the side of the shut-off valve just as if I hadn't given it any love. I suddenly realized that I hadn't looked at the valve very closely before and just assumed that the leak was on one of the pipe connectors etc. But now I thought I had to buy a new shut-off valve. Due to most posts on the net regarding this problem talking about replacing the shut-off valve, I went to my Merc dealer with the idea that I'll just buy a new valve and replace it. Until I heard the price... ZAR2600 (about US$400!).

So I decided to have another look at my old shut-off valve. Now I noticed that it is possible to remove the two caps on the ends of the valve by driving out two pins on each side. This revealed two very brittle and squared-off o-rings. I went to my local o-ring shop (Bearing Man), as Merc told me they only sell the shut-off valve as a unit and have no parts internal to it. The guy at Bearing Man said that these squared rings must have been round-shaped around 1994 or so and sold me 2 o-rings (2-214 Viton o-ring, 3.5mm X 25mm) at ZAR20 (US$3). These turned out to be too thick, but I was able to install them(the shop being closed on Saturday afternoons), with much effort, grease, elbow-grease. I think a 2.5mm or 3mm thick o-ring should work much better.

After reinstalling the shut-off valve and cranking the engine for what seemed to be 2 minutes (30sec break after every 30secs) it started and has not dropped a single drop of diesel from that area. (10km test-drive)

Let's hope that it stays that way and that I'll have a car that starts easliy tomorrow morning!

If it starts leaking again I'll replace those two 25mm o-rings on the shut-off valve with 2.5mm thick ones first before looking at anything else.

I also learnt a few things, such as what huge difference it makes working on this dirty job with latex gloves. Never used it before but for this job it is definitely worth it!

I also think that the OM606 engine in the E300 Diesel (we didn't get that car down here in South Africa) has the exact same part and problem.

Below are some pictures of the parts in question for anyone else suffering the same problem:

Side-view, with shafts driven out, caps off, and (flat, brittle) o-rings removed:


Side view close up where you might be able to see the numbers:


Right-hand(engine side) view:


Front side(of car) view:


Rear side(of car) view:


Old(top, square) and new(viton) o-rings:


One of the transparent fuel lines(as reference of how the clips and seals look & work):
 

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#4 ·
Follow up to shut-off valve seals replacement

It turns out that the issue was still not solved, as the too-thick o-rings that I'd installed started leaking again after about 6 weeks. I opened everything again, and saw that my forceful installation of the 3.5mm o-rings damaged them quite a bit, shearing off edges off the o-rings almost all round. I also had a real good time trying to get the damned caps with oversize o-rings out again!

So Bearing Man supplied me with 2.5mm o-rings (didn't have 3mm at the time), which I tried, but they were too small. It leaked like crazy when I primed it and I didn't even try starting.

Went back to Bearing Man a 3rd time, and they found 3.0mm thick o-rings, but made from some other material (used on brake fluid based systems?). These fitted perfectly and after installing them and reassembling everything the car once again started after about 2 minutes of cranking. After that, about 3 days in a row the car would start easily.

Then this morning, it started, then died, then took quite long to start again (maybe 45 secs? - quicker than when it's leaking). Haven't checked properly for leaks but there's no air bubbles in the fuel line. I'm thinking to myself: WTF?
 
#6 ·
it was the small seals

It turns out that through all the removing & installation one of the small pipes' seals were indeed pinched and was sucking air. Luckily I have by now accumulated a huge stockpile of extra o-rings to pick and choose from ;)
It started twice now without drama - a good sign
 
#8 ·
I used jeweller's screwdrivers to pry the cap out, from multiple angles - including the holes where the locking pins came out.

After I installed the oversized (3,5mm) o-rings, and had to remove it again, I forced the smallest jeweller's screwdriver between the housing and the cap and lifted it out millimeter by millimeter from various angles. Maybe I can explain better or draw a picture sometime.

It did damage the housing a bit, but as long as the damage does not go too deep (beyond the seal) it should not matter. By the way, the "caps" have cavities in the sides, in between the entry and exit holes of the pins, and only about 3mm "in", so these will be the best areas to focus on getting you small tool in.

geez does that make any sense?
 
#10 ·
Dear wimc, thanks for the wonderful job and pictures from 9/11/2010. It really helped

My car: Mercedes C W202 Engine: OM 605 Year: 1998
Problem: Air intake in low-pressure diesel tubes.
Symptom: difficult to start after a day or a night stop, mainly if the tank was less then 50%.

First: I replaced rubber tubes among the injectors; the problem remained.
Second: I replaced the 6 plastic transparent tubes; the problem remained.
After I searched the net for similar problem and I found your description, and that’s it. It’s the shut-off valve O-rings. I replaced them and everything is fine.
Your guess is right; the o-rings diameter is 2,5mm. Should explain to the dealer that’s material for diesel, not for oil. This spare is a Bosch spare not a Mercedes spare. In my opinion, Bosch soon or later gives problems! And you can’t find a bit of technical information about these products! They are more interest to sell then to inform.
On the other hand Daimler Benz is the most honest car manufacturer; spares no Mercedes made, keep two references; you chose the one you want. Besides, if you need a bolt, Mercedes sells you a bolt. You don’t have to by the all kit, as in many other brands.
 
#11 ·
Thanks

Thank you for the very clear pictures this problem has been causing major problems not due to fuel leaking the leakage is very slow but it has been allowing air into the system and we had been unable to trace the fault. MB were not a lot of help insisting the car had an electric lifting pump in the tank which it does not have:mad::thumbsup: and never suggested it could be a worn 'o'ring in this part every other 'o'ring has already been replaced as just about every pipe but after seeing these pictures we discovered just a slow leak which must be where the air is getting in thanks once again.:):thumbsup:
 
#14 ·
I'm very glad that it helped some people. I sold my non-turbo Merc and bought a 1997 C250TD, which has now developed a fuel leak... I doubt it's the same problem but soon I'll be working on this messy part of the car again.

I went to the local merc-dealer in the afternoon to get a new square ring, the one on the engine side. They only had o-rings. They had actually never heard of/seen a square ring. And mine is not only square, it is conic. So I hope the o-ring will do.

I just need to pick up a couple of o-rings for the caps.
----
Update Dec. 5 2012:
I have changed 1 oring on the front, and 2 orings on each side. The 2 rings at the caps were square too, but I fitted regular rounded orings.
Btw my authorized, local Merc-dealer does not sell the orings for the shut off valve; on the entire valve. And that is 1,400 DDK, some $240 USD.
Tomorrow I'll install the valve in the car, and hopefully it doesn't leak anymore.
finnr, Did it stop leaking? The price for the complete valve is outrageous and once you've seen what's in there the price seems even more crazy!

I seriously think that the rings were never intended to be squared off or conic, but instead that a round o-ring becomes moulded to the shape of the casing over 15 years of continuous heat. Then when it degrades to the point where it cracks or shrinks to let some air in, your problems start.

Does your car really have 605,000km on? What major work have you had done to it?
 
#13 · (Edited)
Thanks wimc, excellent post.

I have had the same problem for some time now. A couple of weeks ago, I changed all the o-rings on the seals. That didn't help.

This morning I managed to take the shut-off valve off. And after refitting it, it leaked even more than before.

Tomorrow I will take the shut-off valve apart and hopefully solve the problem.

I went to the local merc-dealer in the afternoon to get a new square ring, the one on the engine side. They only had o-rings. They had actually never heard of/seen a square ring. And mine is not only square, it is conic. So I hope the o-ring will do.

I just need to pick up a couple of o-rings for the caps.
----
Update Dec. 5 2012:
I have changed 1 oring on the front, and 2 orings on each side. The 2 rings at the caps were square too, but I fitted regular rounded orings.
Btw my authorized, local Merc-dealer does not sell the orings for the shut off valve; on the entire valve. And that is 1,400 DDK, some $240 USD.
Tomorrow I'll install the valve in the car, and hopefully it doesn't leak anymore.
 
#15 ·
Yes, the new orings did the job. I have had to buy a new battery though. The old one died completely. In the end, it just kept blowing the fuses in my charger.

Parts prices in Denmark are outrageous. I usually buy parts from www.pwkteile.de in Germany, or I find parts at smaller (cheaper) scrapyards. I actually got the orings from the MB dealership, no charge.

I bought my 250D 6 months ago, it had just passed 600k. I needed a car with at least 12 months until the next periodic motor vehicle inspection.
At the price I got it, alternatives would have been 10-12 years old Skoda Felicia, VW Polo, Fiat Punto, all compacts, none diesel, bad fuel economy, lousy comfort.

New from the dealership until 1994 it was a taxi. The first 250-300k are probably done in the first 2 years. I believe no major parts (engine, clutch) have been changed, no accidents, even the paint job is still nice. Then again, the sun is not as strong here as ie California, or southern Europe. No rust, which is very rare in this wet and cold climate. The last 4 years it belonged to a cancer patient, that at the end couldn't even drive due to bad health. He gave it to his friend: 2 months later his friend lost his drivers license. Had smoked some pot 3 weeks earlier, it showed in the blood test and SLAM - no license.

Next I need to fix the parking break. Everything inside the drum has been removed, actually torn off. Somebody must have used tire bolts that were way too long. I found bits of metal and a spring inside the drum, when I recently serviced the brakes.

Do you know if the drum comes off as a single piece? Or do I need to replace the entire shaft?




 
#17 ·
I bought my 250D 6 months ago, it had just passed 600k. I needed a car with at least 12 months until the next periodic motor vehicle inspection.
At the price I got it, alternatives would have been 10-12 years old Skoda Felicia, VW Polo, Fiat Punto, all compacts, none diesel, bad fuel economy, lousy comfort.
I wholeheartedly agree with you on this point. It's all about comfort.

New from the dealership until 1994 it was a taxi. The first 250-300k are probably done in the first 2 years. I believe no major parts (engine, clutch) have been changed, no accidents, even the paint job is still nice. Then again, the sun is not as strong here as ie California, or southern Europe. No rust, which is very rare in this wet and cold climate. The last 4 years it belonged to a cancer patient, that at the end couldn't even drive due to bad health. He gave it to his friend: 2 months later his friend lost his drivers license. Had smoked some pot 3 weeks earlier, it showed in the blood test and SLAM - no license.
Lose your license for smoking pot 3 weeks before? That's new to me! Things work a bit differently here in Africa I suppose :Smoker:

My father in law had a C270CDI with 550k km on, but it was replaced by insurance when it "drowned" under a bridge during a downpour. The next day the mechanic who wrote it off due to "water damage in the engine" was seen driving it around town, so I suppose it's still going now...

Next I need to fix the parking break. Everything inside the drum has been removed, actually torn off. Somebody must have used tire bolts that were way too long. I found bits of metal and a spring inside the drum, when I recently serviced the brakes.

Do you know if the drum comes off as a single piece? Or do I need to replace the entire shaft?
Sorry I've never opened the rear axle or drums. I have however seen other cars with destroyed drum brakes and it ain't a pretty sight... Good luck with fixing it!
 
#21 ·
Credits to Wimc

Many Thanks for the detailed repair guides from wimc.

Our C250TD had long term symptoms of air in the fuel system, but all trials by replacing fuel line O-rings and even a costly injector pump sealing job was to no avail.

Today and finally our TD lost diesel, yes right below the shut off valve ( before only vacuum leaks were present which we never found ).
The shocking story was that MB asked for R2800 for a replacement valve unit, that triggered me to check the internet.

I got 2x Viton O-rings 3x25mm from All Controls on Voortrekker Rd for R17 today.
Yes they did the job and sealed our leaking valve.

Many Thanks for the detailed guideline on how to repair the shut off valve and save so much money ... I owe WimC plenty beer in Dizzy's in Camps Bay :).
 
#22 ·
see you at Dizzy's

Many Thanks for the detailed guideline on how to repair the shut off valve and save so much money ... I owe WimC plenty beer in Dizzy's in Camps Bay :).
Glad you found it helpful. I'll be right over at Dizzy's ;)

My C250TD is now also leaking diesel - but this time near the tank on the fuel line. It also leaks power steering fluid and engine oil, so the street where I park it is starting to look like an oil spill.

I've been left stranded twice this year due to water in my fuel. I think that's also making my car having a hard time starting at times. The only remedy is to remove the fuel filter and empty it out.
 
#23 ·
I have a 250D with 363.000kms on the speedo and with the same problem, 2 minutes crancking to fill the fuel system. So, where can I get those o-rings?

Thanks for the explanation, it´s great help as I changed all fuel lines the o-rings and the problem still there
 
#25 ·
I originally got mine from Bearing Man in Cape Town here.

But there are many places selling these seals. Best to take samples with you. If you buy o-rings made of Viton for the whole system, you should be able to run your car on veg oil too ;)

The seals for the fuel line was available from the Merc dealers for not too expensive as I recall, but the seals for the shut-off valve had to be got from a 3rd party.
 
#24 ·
I don't know where you are, but you simply go to your next gasket/seal vendor and asked for 2x Viton O-rings 3x25mm and fit them.
You will discover how elastic new O-rings are compared to the old onces. Mine were square shaped and solid and therefore leaking at first air in and finally diesel out.

My C250TD with now 200.00km is running as if brandnew since I replaced both O-rings in the Shut-off valve.
 
#28 ·
hi guys
I have a 202 c250d non turbo and would like to know how to replace fuel filter and bleed the air out,also the previous owner didn't tell me that the injector pump was cracked and it is now leaking engine oil, I have purchased a good second hand part, but I haven't a clue on how to set the timing? Plz advise..
 
#32 ·
Here you can find the OM605 and OM606 stuff.

The full W124 service manual is available, free and legal, here as well. The last W124s had the OM605, albeit never in South Africa.

Personally, while you could follow these adjustment procedures, I tend to stick to the old OM617 300D W123 method, as the settings are the same: 15° ATDC at idle, or 24°±1° BTDC at full throttle - the latter gives a finer adjustment, IMHO
 
#30 ·
Hi guys, thanks a lot for this excellent problem solcing descrioption! -

I have the same problems with starting my C250TD combi 1997, and will replace the o rings tomorrow (got to find them first).

FYI: My C250TD combi with only 563.000 km on it, still going strong without big repairs (only "normal" maintenance/wearing parts replacement).

Took out the catalyst (car still has its original exhaust pipe(!)) and since then it goes like thunder again, all 150 horses present and eager to go!

Keep up the good worK!
Regards from the Netherlands
RvW
 
#35 ·
wimc's pic of the SOV:


Having just performed this repair, a few notes . . .

First, in the picture below, note the two small blind holes in the end caps. They will serve as a visual guide to reinstalling the caps later in the proper orientation. The caps are not indexed to the SOV body, and if the caps are not oriented with those holes just so, the retaining pins cannot be reinserted at reassembly. While it's possible to rotate the caps after assy. using eg needlenose pliers, it's best to insert the caps as close to the correct orientation before pressing them home.

This metal spacer must be removed prior to removing the end cap beneath:


A 3/32" pin punch fit perfectly to drive out the four cap retaining pins. Very light tapping force was required; I held the SOV in one hand, and tapped the punch with a small hammer with the other. The pins slid out easily.


A small screwdriver was used to begin to lever out the end cap, via the pin bores. The cap does not need to be completely removed by this method -- read on:


Once the cap is levered up a bit, a recess in the cap can be accessed on the edge:


A poorly-lit picture of the inside/side of a cap:


O-ring no longer pliable:


View of the stepped bore. The o-ring bore measures 30.5mm:


(Continued in next post)
 

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#36 ·
The cap's o-ring surface is 26mm
The cap's o-ring groove is 3.5mm wide
The o-ring bore is 30.5mm

I ordered three different size o-rings to try (all in Viton** material, hence the 10-pack quantities):
2.5mm width x 26mm ID x 31mm OD
3.0mm width x 25mm ID x 31mm OD * This is the size I installed.
3.0mm width x 26mm ID x 32mm OD

When I trial-fitted the 2.5mm o-ring, it felt as if there was not enough interference fit; the end cap fit too loosely, IMO.

I installed the 3.0mm x 25mm ID o-ring, using grease liberally on the ring prior to install, and was just able to press the caps into their bores using strong thumb pressure.

Picture of the 3.0mm x 25mm ID o-ring installed on an end cap:


The end caps properly aligned (note the two blind holes in each cap), the retaining pins inserted almost with my fingers only. I tapped them into place with a screwdriver handle.

** I am running commercial B99 biodiesel, so Viton is required in my application; nitrile (Buna-N) is just fine for petrodiesel.
 

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#37 ·
I have air in the fuel lines and like you said its only there and hard to start in the morning after it has been sitting over night.
i just got it back from i mechanic but they couldn't work it out and didn't really know much about old diesel models 1995 C250
They said they replace the O rings but now that i have read your post i don't think they replace the shut off valve O ring.
Witch just makes me think it must be that. Because my car runs like a dream once it is warm and through the day.
Ok guys i am girl that is really good with cars and have pulled many apart and rebuilt and i feel where i take my car to get fixed they just want my money. i have read over how you guys have fixed it and I am sure i could do this with a little help.

thanks Vicky
 
#39 ·
thank you so much for this post and all the feedback as well. the engine from my W202 C250D automatic was stalling and sometimes just turned off. The problem was the electric plug loose on the pump valve. It looks the guy that remade the electrical wiring broke the plug's clip so it is kind of loose. Also I'm seeing diesel leaking so will replace the orings as you explain. Not so easy to remove the valve... lets see how handle myself.
Greetings from Portugal.
 
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