Two or three years ago I replaced all the clear hard fuel lines on my '97 E 300 D with new lines from the dealer. Now the fitting on the outlet of the prefilter is wet with fuel. I'm puzzled as it seems way to early for the o-ring to have given up, and I thought the prefilter was on the suction side of the fuel system and would be more likely to suck air. Perhaps it is, and just bleeds fuel when shut down. I have a few o-rings bought from Mercedes when I bought the lines, but I wonder if there are better ones to use on these fuel lines. I'm thinking that the ultra low sulfur fuel might have something in it that the o-rings don't like. I saw that A u t o h a u sAZ had some for $3 each, so they must be quite special. Does anyone have any information on these fuel line o-rings and recommendations as to what one should use with today's fuel?

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'97 E 300 D

I don't know about your particular car, but as you may know, biodiesel, especially in higher concentrations, can degrade some types of rubber/plastic. Are you running any biodiesel in it, other than the ~5% which may be mixed in to petroleum diesel?

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Marshall Welch
Seattle, WA
1982 300D-T

Not that I am aware of.

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'97 E 300 D

See link for sizes and counts.

OM606.962 o-ring size

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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 link. I thought there were only two sizes on the fuel lines but it looks like there are three, at least on the turbo version. I have the 606-912. My replacement lines already had the o-rings on them, but if they were manufactured with the wrong size o-rings, that might explain why a couple are weeping.

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'97 E 300 D

Doubtful that the orings are the wrong size if they were OEM fuel lines. More likely they are deformed (they become squared or oblong) or the Buna rubber compound has deteriorated due to heat and chemicals in the fuel.

Viton is a harder/denser compound which holds up longer to heat, fuel and biodiesel. Seems to work well and last 2-3 times longer then the Buna orings.

The white horseshoe clips on the fuel lines are spreaders used for removal only. Once the line is installed and seated, they should be pulled back so that they are loose and floppy.

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Terry Allison
N. Calif. & Boca Chica, Panama

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

I believe I fixed the fuel leak today. The fittings on the fairly new fuel lines were not actually leaking, just wet from fuel leaking out from the return fitting at the top of the filter housing. The fuel was running down the back of the housing to the pre-filter outlet and dripping off the housing and being spread around by the wind from the fan. When I changed out the lines a couple years ago I didn't change the o-ring on the return fitting. Dumb! I discovered today that the parts stores no longer have those compartmented boxes of o-rings. I found a fair fit in an assortment pack. I'll have to order a full set.

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'97 E 300 D