Why do my injector return hoses keep leaking?
 

The injector return hose going from the front injector to the fuel distribution tree started leaking about 400 miles ago. I had some fuel hose sitting around from the last time this happened (to a different hose), so I simply replaced the hose and washed the diesel off of the engine.

Well, I just filled the fuel tank up today (which may or may not be related, as I do tend to slightly overfill the tank). After driving the car about twenty miles I began smelling diesel again. I stopped under a light in a parking lot and looked under my hood and the exact same hose is leaking again. What could be causing this?

I suppose that there is a chance that the hose I installed was bad, but why would it have held for 350 miles before giving out? Would the fact that I overfilled the tank have something to do with it? Or do I maybe have a problem with that fuel injector? I don't know, but please offer some suggestions. It is quite embarrassing when I am out with a lady or with friends and my shiny black Mercedes starts smelling like diesel.

Two comments:

1) Get some fresh hose and try again.

2) Find a lady that likes the smell of diesel. She'll come from a good family - one that owned Mercedes diesels.

:)

Ken300D

Ken,

1) Going to install some new hose on Monday. I was a little rough installing the hose and I think that may have led to its failure.

2) I currently live with a girl who likes the smell of diesel. She drives the 280SEL, but only because her dad will not relinquish his car. Her father drives a 1976 300D with about 270k miles on it. His father bought it when it was new.

I personally don't mind the smell of diesel, but it tends to give me a headache when strong fumes are blown into the cabin.

I've got the same thing going on with my '82 300D. Its either the return hoses or the injectors themselves leaking. It got worse suddenly when I ran a full bottle of Red Line DFC in a tank - maybe it cleaned out something that was plugging the leak.

So the easiest thing to fix first is the return lines.

I've been looking at the wet areas, trying to decide if its the injector or the return hose. Can't tell for sure, but it looks like the whole injector is wet - leading me to believe its the return hose which attaches at the top.

Ken300D

ARRRGGGHH!!! I replaced the hoses on Monday. The leak dried up. I drove the car about 80 miles. The diesel fuel evaporated off of my engine. I have now driven about 130 miles and there is a leak again!!! The hose is wet, along with the area where the hose meets the injector. Am I incapable of installing fuel hose, or is my injector leaking in that area?

Being a diesel fuel shop mechanic, I have dealt with many of these problems on MB's and VW's.
Most car owners do not purchase the correct hose. We have the metric braided hose that you need to correctly fix the problem.
In rare cases, the "pressed" in fuel return pipe on the injector is causing the leak, but will leak again soon after the car is driven.
Most likely, the "wrong" fuel hose is used and it inflates after it is heated so long.

Good point. You should get the return fuel hose from a Mercedes parts place. I just got a bunch of it from FastLane. And I understand if it is in good condition it will be nice and flexible rather than tough and brittle.

Not trying to use vaccum hose, are ya? :)

Ken300D

leaking fuel hoses....
 

I hear you all as my '77 is the the same way (new injectors, and replaced lines)

FWIW, I had wondered previously with my car if the hoses (which seem to be a semi-soft metal) became mildly cross-threaded if they're not seated just right when screwed on *shrug*. The injectors (aside from spotty re-build quality) seem to be pretty sturdy on the threaded ends. I can't speak for W124's though.

I still see a slight weeping from two problem injectors/hoses, but funny enough, they seem to come and go (?)

- Ryan

I am using the new beige braided fuel hose that the MB dealer sells. I'm quite particular about using genuine parts. I just relaced the hose this morning for the third time. I have driven about 50 miles today and the leak seems to have dried up, but last time it took 130 miles so I guess I will wait and see.

don't get hosed!
 

I replaced mine with the black
colored stuff once and it lasted 500 miles
before it began to leak.
I then replaced it with the beige braided
stuff from the dealer.
No problem over 500 miles.
Replace the plug at the end of the
row. That may be the cause of your leaks.
I wonder if air in the line can cause
leaks?
Is your hand pump (primer) leaking?
Maybe that needs replacement??
I had mine replaced same time the new braided hose
was installed.
Good luck.

Don't do what I did with the injector return hose task today. I decided to pull off the one line that looked the worst. Sure enough, it was rather brittle, and broke rather than sliding off the injector. No problem, just a little more work to get the piece off.

Well, I'm great for doing maintenance on my vehicles in stages, since it helps to get away from the job and think about it. So, I didn't put on the new hose right away.

Whew! Thankfully I had another reason to go back into the garage. Diesel fuel on the floor! Maybe only a few tablespoons, but it sure was a mess. I think there was some kind of siphoning action going on.

Two hoses were brittle, two were in good shape, and the little end piece with the plug was brittle. Appeared to be the brittle ones that were leaking.

Moral of the story: Once you tear the old hose out, put the new stuff on right away!

Ken300D