Injection pump leaking oil

[MikeL43]

I have read a number of posts in regard to the injection pump but not one that directly addresses my problem.  I must again thank JA for his posts on this subject despite my inability to find an answer to my problem.  I have a very late 250 SL (SN 5167) which has an injector pump with a dipstick.  I finally got my car back after a mini restoration that took 14 months (new paint, etc, the results are fabulous).  The problem I am having is that I get a substantial puddle of oil under my car after I have driven it a few miles.  I have traced the leak back to the red OIL vent on the injector pump. When I take the cap off, the car is not running,  I get a trickle of oil out of the IP vent.  When I checked the IP oil with the dipstick a significant amount oil came out of the dipstick hole.  I had the oil and filter changed right before I got it back and after I drove it a short while I noticed that the sump dipstick indicated the sump was overfull.  I'm not sure what to blame for the problem, the 14 months of sitting, the overfull oil sump or a UFO.  Based on the many posts that I read I am inclined to think that the oil drain hole from the IP to the sump may be clogged.  Is this a reasonable assumption and more importantly what can I do to alleviate the problem?

[scoot]

No, that's not a clogged passageway.  There is no connection between the oil in the injection pump and the oil in the sump (on your model and year).  Either it's been overfull for a while or, more likely, gas is contaminating the oil inside the injection pump and coming out from the vent.  Try removing all the oil (syringe, spray pump tube, etc) by sticking suction down to the bottom of the injection pump via the vent cap (which is actually the fill cap).  Then fill it with the right amount according to the tiny dipstick on the pump.  Take a good look/smell at the oil that you remove from the pump - is it contaminated with gasoline?  If so then I don't know of a remedy other than a pump rebuild.  Perhaps others can give you better advice.

[ja17]

Yes the early cars had IPs with no oil return to the sump. Leaky seals in the IP are usually the culprit.  Bringing the car back to life after a rest may help soften the old hard seals in the IP.

[MikeL43]

Thanks for the suggestions.  As far as the gasoline mixing with the oil I have ruled that out as there is no gasoline smell with the oil and the level of oil on the sump dipstick goes down proportionately with the amount of the leak.  In regard to the gas mixing with the oil I have over 45 PSI of oil pressure and about 20 PSI of fuel pressure which, according to other posts rules out the likelihood that gas is mixing with the oil.  I have noted that since nearly a quart of oil escaped from the IP dipstick the oil is no longer visible through the vent hole in the IP labeled OEL.  After a short drive the oil level is still not visible through the OEL vent though a lesser amount still leaks out of the IP dipstick hole.  I am inclined to think that JA has the right idea and that the O rings in the IP dried out after the car sat for 14 months and may, hopefully, be resurrected with use.  In the event this problem doesn't fix itself I guess I will have to have the O rings replaced.  In that event who does the forum recommend and what is a ballpark estimate of what it will cost?  TIA
   

[Tyler S]

You shouldnt be able to see an oil level via the “oel” breather. The rear portion of the IP only holds a small amount of oil. You need to start from scratch with the proper oil level. Evacuate all of the oil via the dipstick port on the back of the pump. Refill to the proper level on the dipstick and retest. Unless there is some sort of severe mechanical damage, there is no way for crankcase oil to migrate to the (rear) portion of the IP. The small oil line in the front of the IP only supplies a very tiny amount of oil to the IP piston galley. There is no direct connection unless the pump is very worn out. Then in which case the oil in the rear would be fuel contaminated as well. Is it possible someone filled the IP as the saw “oel” and didnt know any better?

[perry113]

Sounds like your ready to pull the pump and send it out.
It's not that hard to do.
Set engine at 20ATDC on cylinder number 6. See your shop manual for further details.
Robert Fairchild has done several pumps for me and in fact has the one for my 1966 230SL barn find as we speak.

[ejboyd5]

Not yet time to consider removal of the injection pump.  As has been previously stated, the injection pump lubrication system is isolated from the engine lubrication system.  The best diagnosis for your problem, if there is a problem, should begin with returning the injection pump lubricating system to its original condition by evacuating all present fluid and refilling with the proper amount of oil. Do not overfill to the point where oil spills out if the fill tube, but fill only enough to bring the oil level to the "full" mark on the injection pump dipstick when it is fully seated in the fill tube.  I've always found it easiest to add fluid to the injection pump by using one of those old style oil cans with a flexible spout and a trigger lever that squirts a small amount of oil each time the lever is pulled.

[MikeL43]

I have considered all of the suggestions offered, many thanks.  I believe that JA has diagnosed the problem correctly, that is the IP has leaky seals.  I have done the following:  evacuated the IP oil level to the proper level on the IP dipstick.  No gasoline smell was detected in the oil that was removed.  I subsequently drove the car around 100 miles and checked the IP oil level and it was again seriously overfull and the crankcase oil level was less than before.  In view of this  I have concluded that the problem is probably the IP oil seals.  Unless someone has a serious argument against my conclusion I am preparing to get the IP checked out.  The only suggestion for the repair of the IP pump thus far has been Robert Fairchild whom I haven't yet got a phone number.  Any other suggestions, anyone have a contact number for Robert? TIA.

[rjmarco]

FYI, I had my FIP rebuilt in the Los Angeles area (Santa Ana) at Diesel World.  This was in connection with getting my engine rebuilt at Metric Motors.  They coordinated the FIP rebuild while the motor was being rebuilt.  I was satisfied with the end product on both. 

[jameshoward]

I have considered all of the suggestions offered, many thanks.  I believe that JA has diagnosed the problem correctly, that is the IP has leaky seals.  I have done the following:  evacuated the IP oil level to the proper level on the IP dipstick.  No gasoline smell was detected in the oil that was removed.  I subsequently drove the car around 100 miles and checked the IP oil level and it was again seriously overfull and the crankcase oil level was less than before.  In view of this  I have concluded that the problem is probably the IP oil seals.  Unless someone has a serious argument against my conclusion I am preparing to get the IP checked out.  The only suggestion for the repair of the IP pump thus far has been Robert Fairchild whom I haven't yet got a phone number.  Any other suggestions, anyone have a contact number for Robert? TIA.

Joe is (obviously) correct. Fuel is mixing with your oil. Been there. I had to have my pump rebuilt for that reason. Early cars have no line, thus the oil in the pump is isolated. Your pump needs to be rebuilt if, after 100 miles, it's overflowing having previously been at the correct level. It's increasingly hard to find good places to rebuild these pumps. If you are struggling, take a look at diesel fuel pump rebuilders. Same sketch, but there are many more of them.

[707dieseldean]

Here is the link to Jerry Fairchild Fuel Injection Center:

http://www.fuelinjectioncenter.com/about-jerry-fairchild-industries.htm


Just had my pump done by him and very happy with $ and outcome..

[MikeL43]

I just had a pleasant conversation with Robert Fairchild (if $800 for a rebuild is pleasant)  and will send him my IP to be rebuilt as soon as I can get the pump off of the car.  He said he was very busy and the turn around time was about a month.  I thought I would pass this information along since it may be of some use to people checking the Forum and as everyone has been so helpful.  Robert also said that Hans (in New York I think), who rebuilt my fuel pump passed away recently and that his son was trying to keep the business going.  Hans was very interesting to talk to on the phone, we have lost another good guy and a lot of institutional knowledge.  RIP

[Shvegel]

Maybe Joe could chime in here but there are only 2 paths for fuel to reach the oil in the IP.  One is through the wall betwen the piston and cylinder(Barrel) in the elemants.  This would most likely be a long term wear issue and not usually result from sitting.  The other is at the top of the cylinder at either the area where the delivery valve (Outlet check valve) meets the cylinder (which is sort of like the head on an engine except no gasket) or where the delivery valve and output fitting meet.  There is a nylon seal between the barrel and the output fitting and there is a chance that this seal was disturbed when the fuel injections lines were removed.  I would try two things before I sent the pump off.  The first would be to remove the lines then loosen and retighten the output fittings to the correct specification which Joe has in his head.  The second is to replace the seals under the output fittings.  This is more involved since it requires at least in my opinion removing the pump from the car and laying it on it's side for removal of the output fittings.  Seals are still available from Mercedes last I checked and I am more than happy to lend you the check valve removal tool.

[Benz Dr.]

Joe is (obviously) correct. Fuel is mixing with your oil. Been there. I had to have my pump rebuilt for that reason. Early cars have no line, thus the oil in the pump is isolated. Your pump needs to be rebuilt if, after 100 miles, it's overflowing having previously been at the correct level. It's increasingly hard to find good places to rebuild these pumps. If you are struggling, take a look at diesel fuel pump rebuilders. Same sketch, but there are many more of them.

All of our cars have oil lines. Early cars don't have a drain back into the engine which is what you might be thinking about. 

[Benz Dr.]

I just had a pleasant conversation with Robert Fairchild (if $800 for a rebuild is pleasant)  and will send him my IP to be rebuilt as soon as I can get the pump off of the car.  He said he was very busy and the turn around time was about a month.  I thought I would pass this information along since it may be of some use to people checking the Forum and as everyone has been so helpful.  Robert also said that Hans (in New York I think), who rebuilt my fuel pump passed away recently and that his son was trying to keep the business going.  Hans was very interesting to talk to on the phone, we have lost another good guy and a lot of institutional knowledge.  RIP

Although I never met Hans in person, I did get to know him well enough. He did about 25 pumps for me over that many years so I'd say he was a considerable asset to my operation. He certainly helped me through some small but irritating problems and some larger ones too. Good guy that will be missed.

[Shvegel]

I have been to Han's shop many times over the last few years as it was near where the boat I work on spends it's Summers.  He was really passionate about his craft and once I revealed my respect and fascination for the design of our injection sytem his eyes lit up and I was treated to a full tour of the shop. 

The one thing that really stuck with me in all my visits there was the number of times he was on the phone talking people out of rebuilding their pumps. He was a very stong advocate of, "If it is working well then leave it alone."