Single Large Air Bubble in Clear Fuel Line

[pberku]

Car is a '95 E300D OM606. This model has a self priming fuel system.

Lately I noticed that when I start the engine when stone cold, and if I quickly press and release the accelerator pedal, it will hesitate. The symptom goes away after a about a minute or so, it never does it when the engine is warm. Otherwise, even when stone cold, it starts, idles, and drives fine.

Today I noticed that within a few minutes of shutting off the engine, a SINGLE air bubble starts forming in the clear fuel line leading to the fuel filter. It subsequently progressively gets larger. I don't remember seeing that before, but nor did I ever look at it very closely. I don't see any small air bubbles as such, Just ONE big bubble.

Could this single air bubble be the cause of the symptoms that I described in the opening paragraph. Is it normal to have an air bubble in this fuel line? If not, where do I start looking for the cause?

I don't have any obvious fuel leaks. I do however smell diesel fuel, somewhere under the intake manifold towards the front of the engine, behind and below the main fuel filter area. This smell however has been there for over a 2 years, and has not gotten any worse. So I am not sure if its even related. It may even be normal Diesel fumes.

Since, apart from the described symptom, it starts, idles, and runs well, I don't mind waiting for the leak (if it is a leak) to get worse, and make itself more evident.

Any suggestions?

Thanks

Phil

[compress ignite]

I'm guessing ...but it will not hurt to check.

[t walgamuth]

definately does not sound normal. prob is causing prob.

above post sounds correct about leak.

tom w

[deltajetfixer]

I have a 1" "bubble" form in the clear line going to the prefilter EVERYTIME I shut off. It is full of fuel with no "bubbles" or air voids when running. None of the other lines exhibit this phenomenon.

All lines have been replaced due to my glowplug replacement so I know they aren't leaking.

I have no problems. I consider it normal for my car. Starts easy and runs great.

If you have a leak, you will have a STRONG, bordering on intolerable diesel fuel smell and at least a drip. I suspect you're smelling just the characteristic "Diesel Smell".

If all you have to do is let the engine run for a minute after starting to smooth out, I wouldn't worry about it. Have you run any additives in it like Powerservice or RedLine?

[pberku]

That's exactly the size of bubble that I have as well. Also in the identical location that you describe. So thanks for your feed back. I'll now consider that to be normal, especially since I don't see a stream of bubbles while the car is running.

I will however go back and check for a possible electrical problems causing my issue. Possibly wiring harness related. I MUST find it.

Thanks again,

Phil

[Hatterasguy]

Replace all of the clear plastic fuel lines outside and underneath the intake manifold. I am more familer with the turbo 606's and they are set of a little different. But their should be a bunch of those clear plastic fuel lines behind the fuel filter in that area. They leak and need to be changed every few years. Do not touch them unless you have new ones on hand! They break!

My friends E300D had the same problems and a new set of fuel lines fixed it.

[pberku]

I just looked at my clear fuel lines again, and although I do see a 1" air space that forms within minutes of shutting off the engine. Its the exact scenario, and same location reported by "Deltajetfixed" in the previous post.

The strange thing is that about 30 Min. later the fuel starts creeping-up the clear fuel line again, and completely fills the line. The bubble that formed previously, may have now been pushed by the fuel to the inside the fuel filter, but I can't tell for sure.

I'll assume for now that this is normal, and not due to a leak. However, I will change those clear (now brown, almost opaque, and hard as a rock) fuel lines next time that I need to have the Intake Manifold off.

Phil