I recently did some work to my 1999 E300D, to include having the injectors rebuilt, installing a new IP lift pump and overflow valve, replacing all plastic and both rubber feed/return fuel lines, as well as replacing all the glowplugs. Did a few other things while in there, such as replacing both fuel filters.

I replaced all the original Berus with Bosch about 50k miles ago, and already had one of the newer Bosch fail, even though the original Berus were fine at 140k miles. Figured I would do some PM and replace them before failure, but it was unfortunate that I used Bosch GPs. So, out with the Bosch and in with all new Mercedes branded Berus.

During the course of the work, I had a couple questions come up, and I wanted to see if anyone could provide some answers and recommendations.

1) I am unable to keep a little bit of air from entering the plastic fuel line that goes from the fuel heat exchanger to the pre-filter when I shut down the engine. I have gone through two new pre-filters and two new o-rings, just in case that was the issue. I have removed and reinstalled the prefilter to see if I could get it to seal better with no luck. It does not seem to have any adverse effect, but it is annoying. I even loosened and retightened the primary filter just in case air was coming in that way. No luck. I am wondering if I have the o-ring on wrong or something, or if air can enter that location in a different place? Pictures included to show air in line and o-ring position.

2) As part of the glowplug service, I started the engine a couple of times without the intake manifold installed to get the engine warm to aid in GP removal. I observed some "smoke" rising up out of the charge air pipe coming from the turbo at idle, even more with some revving. It seemed to me that this air should be cleaner, as it is the source of combustion air to the motor. With the manifold off there in no longer a connection to the EGR, so it can't be exhaust being fed back to the IM. I am wondering if this is normal, or could it be bearing and seal wear at the turbo allowing smoky motor oil to enter the charge air pipe? Pictures included, but it is really hard to see the "smoke".

3) Also on the charge air pipe, there seems to be a lot of oil or something oozing from the weep hole located at the bottom of the EGR, which runs down the charge air pipe and gets soot around the MAF attachment point. Again, just wondering if this is normal?

With the all the work that was done, all the pinging and nailing is gone, and the car seems to be running really well. It's about as quiet now as 100k miles ago, which is leaps and bounds quieter than any W123 I've ever had.

Thanks for any insights.

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I had a similar issue with the pre filter as you are dicribing that was solved by the addition of a washer between the bolt head and plastic housing

__________________
Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

There is a small metal plate between the bolt head and the plastic top of the end of the fuel line that comes installed from the factory in order to press the pre-filter down into the filter console as the bolt is tightened. It can be seen in the first photo in my original post and modified photo here.

Were you missing that plate, or did you install the washer in addition to that plate?

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Yes, in addition to. Get just a little bit more squeeze out of that bolt.

__________________
Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

The tabs on the pre filter washer go flat because the metal is soft, just bend them back over a bit , once they go nearly flat then you can do the bolt as tight as you want but it will not put any more pressure on filter.
I found it best practice to put another o ring (same size) above the one it already has and this will help it seal better.

The sensor in pipe is the charge air temp sensor, most likely just needs another o ring seal fitting to it. Squeeze the tabs together and it just pulls out.

I don't think my problem is with that o-ring. The area is getting mucked up because there is a small weep hole on the exterior bottom of the round "baffle" or whatever it is, that is on the side of the EGR section, and has the larger of the two vacuum lines attached to it.

This weep hole drips oil or whatever it is onto the outside of the charge air pipe. See pic.

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I have an extra o-ring, so I might try to add another one, or try the washer trick. I can't imaging there being enough space for two o-rings, since it seems one takes up almost all of the available space already.

Since it may be the tabs bending due to soft metal, what about just flipping the pre-filter washer over?

Put a pipe on the egr and put vacuum to it to check that the diaphragm is still working ok.

I presume if it is bad then it will leak from the weep hole ? .

The second washer just goes up above the original one and then when you fit filter it just gets squashed into place