Perkins 4-108 lubrication oil into the diesel fuel

[RussellJ]

Hello all,

I just got an email (via satellite) from some friends down in Baja (Bahia de los Muertos to be specific). My internet searches only found the usual diesel-in-oil scenario. Hoping somebody here might have some idea what's going on:

"We have a strange problem with the Perkins 4-108. I am getting lubrication oil into the diesel fuel. This is really strange, I have never heard of it happening before. (The other way diesel into the lube is a failed lift pump, but we have the opposite, lube oil into the diesel return).

I figure it still has to be either the lift pump or the high pressure fuel pump, but I can't figure out how it would be. Can you look around on the net and see if you can find anything?"

Thank you very much for any advice you might be able to offer.

[Lepke]

How did they determine motor oil in the fuel? There is no reasonable path. Wherever fuel and oil are separated by a seal or diaphragm, the fuel is at higher pressure. Any failure would cause fuel to go into the oil.
It could be the fuel tank was sturred up and sediment is in the fuel, changing the color. Or they bought some nasty old fuel.

[a64pilot]

Well they were pretty specific, they said lube oil in the Diesel return.
However I have never heard of it either, if you had asked me, I’d tell you I didn’t think it possible either.

[shakey doug]

When Pintle type injectors wear between the Pintle and Holder the return diesel takes on a dark oil type appearance due to its high carbon content. Seen this many times with Lombardo type injection anti chambers.

[Eigenvector]

Following........Just to understand and maybe learn something.

Normally you notice an increased oil level due to an injector pump problems filling your crankcase with diesel fuel. IE High oil level.

The inverse........ The tank is filling while running? 5 qt oil filling 50gal fuel tank in a measurable amount?

Am I missing something here?

[shakey doug]

Cannot see any reference to volume increase/decrease or have I missed something?

[RaymondR]

The most likely place for the contamination to be occurring is through a small hole in the fuel lift pump diaphragm, particularly if the lift pump has to draw the fuel up from a tank at a lower level.

[shakey doug]

Lift pump actuating lever area is splash fed only nil pressure, fuel pressure within pump approx. 4/8 psi any fuel leakage would and does go to sump.

[RaymondR]

Originally Posted by shakey doug

Lift pump actuating lever area is splash fed only nil pressure, fuel pressure within pump approx. 4/8 psi any fuel leakage would and does go to sump.

Nope, on discharge stroke pressure differential is across diaphragm into sump but on suction stroke across diaphragm from sump to fuel side.

[wolfgal]

For what it is worth, i just checked notes i took at a Diesel Engine Maintenance course i took with the Power Squadron last year. they read:

a worn diaphragm can leak oil into fuel, if/when lever rising