White smoke, lack of power, caused by clogged fuel filter!
 

Well, while I wouldn't have believed it I can tell you from my own personal experience this week that a clogged filter did cause the white smoke from my '98 E300 DT. Starting this past Thursday morning the car was running oddly. I first noticed it about 6-7 minutes into my trip out in the morning, the car lost power severely and white smoke was clearly visible behind me. I was able to pull over into a parking lot, shut the car down and restarted it and it ran much better...still not right but better. I could feel it struggling to make it up steep hills which it never did before.

The next morning it was even worse...got on the highway that is about 2 miles from my house and the car almost died with great big clouds of white smoke out the rear end...had to pull over and again shut down and restarted it. Now it was clearly running poorly and exhibiting fuel starvation. I nursed it to the MB dealer and bought a spin-on fuel filter and prefilter with new o-ring.

The old pre-filter looked fine and the old o-ring was tight in there as well so there wasn't any leak from that before I changed it. So I proceeded to replaced them both and it has been fine ever since that time, yesterday at noon. I just got back from a 10 mile "first thing in the morning" test drive including high speed merge onto the same highway I had to pull off of yesterday and there was nothing unusual now...so the filter did cause the white smoke, and near-death of the engine experience, I am convinced of it.

I am also convinced that the new ULSD fuel is the cause of the old filter clogging. The old filter was about 20 months old, and it had less than 25K miles on it. I'm on my second "official" tank of ULSD and now I not only had the filter clog issue but the delivery valves on my IP are leaking as well. Stupid ULSD!

Marty,

I am having the exact same issues you are having with my '98 E300D. My IP fuel leak and loss of performance started about 1-2 months before the official ULSD stickers went on the pumps, so I too am convinced that fuel is the issue for me as well. I replaced my fuel filter(s) about 8 months ago so I am hoping they are OK.

Have you considered cleaning the tank screen? I have always experienced a noisy idle at low RPM (< 1600) and have heard that the fuel pressure in the IP delivery system is pretty fussy and pressure wave in the fuel return line can cause this effect. I also have ordered a new belt dampener in case that is the culprit.

I have read some of your previous posts and I too am preparing for a delivery valve resealing with new O-rings and new crush washers so please post your experiences and any tricks you figure out along the way.

Did the new shut-off valve O-ring fix your fuel leak? Mine is still gushing after I replaced mine..

Well the first thing I would do if I were you is replace the spin-on fuel filter as I am convinced mine was clogged by the ULSD, or rather all the crud it loosens up. I now recall one station I was at a couple of months ago that the pump was REALLY slow on and they claimed they had to change the filter twice since they started receiving the new fuel...

I stripped the heads on both of the shutoff bolts so I am going to have to drill them out when I do the rest of the fuel leak repairs after removing the intake manifold. I decided now to wait and order all of the plastic fuel lines and replace them too even though they are less than 2 years old only because replacing the seals on them costs nearly half as much as the entire line does for each one, so I figured I would just start will all new lines, all new seals and do the IP delivery valves at the same time, probably the week after Thanksgiving. For now the car runs great again after changing the fuel filters so I am less concerned about the leaks as they are only a (stinky) annoyance for the time being. Of course if they get worse before then I may be forced into action.

I haven't looked into the tank screen...I really think the main spin-on filter is the one which catches all of the crap loosened up by ULSD. Once I replaced that one yesterday the car was back to being like new again, just smellier.

Oh, and one more thing...I am going to buy a spare spin-on filter the next time I am at the dealer and carry it in my trunk. It only take 5 minutes to change it and the idea of being stranded by a clogged filter is absolutely silly now that I know how fast that can happen it has frightened me into action!

I do have a spare in my toolchest and was hoping to do it next year sometime, but they are fairly cheap so I'll go ahead and do it this weekend. I bought some Lubro Moly Diesel Purge a few months ago and was planning to do it before winter so I guess it is a good time to do that as well while changing the spin on filter.

Funny, I just got back from buying 2 new M6 socket-head cap bolts this morning to replace the near stripped torx bolts on the shut-off valve.

Quick question regarding my fuel leak: The vacuum side of my fuel delivery system is working great - no air bubbles getting in since it starts right up without stumbling. The weird part is that there is a constant leak of fuel from somewhere on or near the IP regardless of whether the car is running or the amount of fuel in the tank. I parked the car at the airport for a few days and there was a pretty serious "puddle" of diesel underneath the car. I'm fairly confident that the shut-off valve was higher than the fuel level in the tank and the puddle was too big to be from the spin on filter. Either way, the car started right up and I drove away with no stumbling! Any ideas?

I don't mean to hijack this thread but by the looks of it alot of 606 owners are having general fuel issues.

I made a short trip with a friend that drove his diesel utility truck. He was having a very hard time making a grade, fortunately traffic was moving slow, I mean 25 MPH, as that was above the top speed of that truck in low gear with a poor running engine. Turned out he had filled up with bad fuel with water or algae or something and the filter was plugged. He said if he had a filter he would change it and we would be on our way at normal speed unfortunately the drive took a lot longer and we were sweating it for a while.

I carry a spin on and a pre filter in my '87 300D now, probably from that experience. And I use the busiest fuel stops where hopefully the diesel is fresh.

I am not that familiar with the 606 but does it have the fuel heater like used on the 603? If so that has been a source of leaks for some. If the area around the IP is clean its pretty easy to spot a leak. The delivery nozzle valve seals are often suspects on the later IP when the engine stumbles at a cold startup. I don't know why but the 617 engines seldom if ever have a problem with delivery nozzle valve seals.

Yes, it does have a fuel heater but there is definitely no leak there on mine. It never stumbles on startup but the entire shut-off valve is completely covered with fuel after a few minutes on the road.

How much fuel do you consider "a good sized puddle"...it doesn't take much and it doesn't evaporate fast so it might have leaked out after you shut down and just sat there. Even an ounce or two of fuel can look like a good sized puddle...it's probably your delivery valves and shutoff o-ring which are leaking just like mine are. I plan on doing them and the plastic lines all at once when I get all the parts together. I just want to be done with it so I will do everything at once and won't have to face a leaky line in 2 months once those o-rings shrink a little bit more from the ULSD.

Funny thing, today my wife calls that she hit a curb about 40 miles from here and needed me to come and change the flat tire...I was a little reluctant about taking the E300 since I just got done "fixing" the filter yesterday but had no choice...so I drove it down and back with absolutely no problems at all...now I've put about 150 miles on it since the filter change so that confirms my clogged spin-on filter was causing all the performance problems, IMHO.

I want to also get nice cap screws to replace the MB crap that held on the shutoff...what length M6 caps did you get???

I agree with what Marty posted about your's. You should be able to tell which of the two areas are leaking pretty easily. Just spray the top milled portion of the IP and delivery valves clean and then run it for 10 minutes. If it stays dry up there the leak ought to be from lower down at the shutoff valve.

ps: If worried about ULSD loosening "stuff" up in the tank try running a tank full of B99 if you can get it, it is a VERY good solvent. Then change filters.

I'd say the puddle was about 4 - 6 oz. of diesel fuel as I have a fairly steady leak of around 1 - 2 oz. per day. I just replaced the shut-off valve O-ring last weekend and it appeared to have no effect. I already have all the parts for my delivery valve reseal job which I plan to do next weekend, so I'll report my results then. The fuel lines were all replaced about 8 months ago so I am not planning on changing those - maybe new O-rings on some of them just to be safe. I might rig together some sort of cardboard shields around the IP valves to see where the leak is coming from.

I think I'll take Terry's advice and run a tank of B100 before my delivery valve reseal and new fuel filter next weekend.

The shut-off valve caps are M6-1.0 x 25mm.

I would guess your leak is from the lines attached to the fuel pump if it keeps leaking after shutdown. It's probably gravity feeding fuel from the tank and leaking out. Since it isn't sucking air I would guess it is the line which goes from the lift pump to the shutoff valve, the one attached to the bottom of the shutoff.

Thanks for the cap-screw spec, I will pick up two of them.

Fuel Leaks
 

My Dad was telling me that he was at a local MB dealer getting parts and the parts guy showed him a print out of sales of various parts. During the first 6 months he sold one or none of several diesel engine seals, yet after June, when the LSD started selling here in NY the numbers jumped and have continued to rise.

On my Dad's 99 E300 Diesel he swapped out the fuel filter after some hard starting and low power issues and found some of the o-rings appeared almost dissolved!

This isn't good. :behead:

Hey Marty.
I normally change out my fuel filter in the fall but have put it off on the 98 E300TD because the weather has been so mild. I did notice it was a little sluggish the other day at low speed/rpm so I'll change it Saturday morning.
I have been running B20 when I could get it so I can't attribute the possibility of a clogged fuel filter to USLD alone.
Cheers