Hey folks. I was wondering if it is normal for there to be air bubbles going from the feed pump to the fuel filter on my '99 Turbo diesel. I was talking to myself in another thread, but this time I'm requesting help. I took my car to the dealership to have the problem analyzed. They changed filters (I could have done that myself) and charger me $150 and said that would fix the problem. The air bubbles are still there. I called the service dept. and told them that the bubbles are still in the lines. They replied that the bubbles are a characteristic thing for that car and that as long as they are not going from the filter to the IP that everything is fine.

Now I'm no MB tech, but I would think that the fuel system is a closed system on anything that involves injection. My girlfriend's '77 240D doesn't have air in the fuel lines and it's thirty years old.

My question is... Is the dealership steering me straight here or are they feeding me a load of hooey??

Thanks in advance for any help.
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1999 E300 Turbo Diesel (Stewie) - MODS: Euro COMAND from Steve MBenz NL, Ceramic Window Tint, Seat Covers and Oil Change
1977 240D 4-speed Manual (Granny) Girlfriend's car - MODS: Audio 30 cassette deck from the '99, Rust abatement, H4 Ciebe Euro lights w/city lights, Pool noodle seat fix
2001 VW GTI 1.8T 5-speed (Buster - R.I.P. 21JUL06) - MODS: 60mph + 1989 Toyota Pickup ignoring stop sign.

Burn Oil, Drive Diesel

Are you experiencing any hard starts? Thats usually the first symptom of a fuel/air leak. Parking nose downhill will help with that.

The only bubble you should see is the line from the fuel thermostat (in cyl head) to pre-filter and then only on shutdown. All other lines ought to be free of air.

Check the o-ring "under" the pre-filter, it is commonly the culprit.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

There are no hard starts yet, but I don't plan on letting it get that far.

Well, the bubbles that I see are in the clear line going to the canister style fuel filter that is closest to the driver's fender. The bubbles tend to occur when I actuate the throttle. They are small, but I was able to point them out to my girlfriend to make sure that I'm not just seeing things. There is a slight miss every once in a while when cruising or minor revving. I've noticed rough spots in the RPM range, but this may just be another symptom. There is some slight nailing, so I will be doing a diesel purge soon as well.

I'm not sure if the fuel lines or glow plugs have ever been replaced on this car.

That line is from the fuel pump to the main filter. You should not see bubbles there.

Sounds like you have a minor leak somewhere.

Check the seal of pre-filter (bolt and hold down), pre-filter o-ring, beneath shut off valve (another oring seal), all clear fuel lines (each has two o-rings) and top of the IP (delivery valve seals) for any wetness.

Let GF sniff for you if you can't find it; they are notorious for finding stinky stuff.

What is the mileage? If the plastic fuel lines are clear and not yellow they are probably fairly new.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Thanks for the tip. Top of IP is dry. Lines are not crystal clear, but I can still see through them. The car has 120k on the odo. Planning on pulling the intake maniford and replacing the glow plugs soon anyway. Looks like I'll be ordering some new lines and some silicone lube for the o-rings just for good measure.

Read up on OM606 glow plugs and make your own descision whether to pull them if they are working properly at this time. There is risk of them being seized and of them breaking off in the head.

Two members last week expirienced just that. One person had a bad plug and so needed to do the job, the one that broke off was not the bad one (he is driving around with 5 new and one half drilled out GP now) and another was performing preventive maint and broke 3 off and damaged the head attempting to drill them out and is shopping for a new head now.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Sounds like it could be time to change o-rings. Check the two on the prefilter, first.

Thanks for the advice TMAllison. No malfunctioning plugs yet, so best to leave alone for now. I will resistance test them in the block if I'm really that worried about it. Just going to clear up the air bubbles for now.

Good advice. When the maintenance foreman is telling me that the bubbles in the line are chacteristic of this model and they are the ones who changed the filter and prefilter for me... sounds like I had better check their work. I've done my own wrenching for some time, but I've been kind of anxious about doing the work on my new one because it's all I have to drive now.

Time to get my hands dirty.

I just wanted to post a big thank you to all those who gave me advice on this problem. I've replaced: lines, o-rings, manifold gasket, clips. An cleaned the intake manifold out... yech!!! I've found a oil leak just under the valve cover trim plate that I will also be taking care of and will replace idler pully/dampner , flex disks and fix some little alert issues with the lights.

One thing I can say for this car. With good fuel delivery and properly cleaned airways... WOW!!!

Thanks again.

Josh

AAARRRRRGGGGHHHHH!!!!!!!

I guess it's time to buy some Viton o-rings for this pig. GRRR.

One thing you can be sure of, when you replace an old seal the pressure on the other seals you haven't replaced will increase...

Yep, that's why all the seals were replaced last time; however, it looks like the new ULSD is more of a PITA than I first expected.
ULSD = Ultra Low Sulfur Diesel.