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engine oil in fuel: where could this come from?

I recently changed out my fuel tanks and noticed that the fuel was black. We also thought that it smelled like motor oil, but that could have been our imaginations at work. Anyway, I sent off a sample of the diesel suspecting asphaltene. The sample came back showing asphaltene, but it also showed flagged amounts of Phosphorous and Calcium and non-flagged amounts of Zinc. The labs comment was that it may indicate contamination with lube oil. Does anyone have any clues what could be happening here.

Also, I have located some asphaltene conditioner in spite of the fact that the Peterbilt and Cummins shop foremans had never heard of it. My question is will I just treat a few tanks or is this something I will have to use on a permanent basis?

The engine is a 1999 ISX that has high oil consumption. I have to add a gallon at about 5,000 miles, then about every 2,500 miles until the next PM. It was rebuilt about 90,000 miles back, but then sat for six years before I purchased it.

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I talked to the service manager at a Cummins shop today, but I am wondering if he heard me right as to oil in fuel and not fuel in oil. Anyway, he said it sounds like I have two problems. He said that on that model of ISX it could be the injector seals leaking. I knew this could get fuel in oil, but didn't know it could go the opposite direction.

Additionally, he thinks I may need a fuel cooler for the asphaltene problem.

Finally, he said that the asphaltene conditioner will not do any good because you will never get all of it out of the tanks.

Thanks for the response MOtech9, The overhead was ran about 70,000 miles back.

For now, I think I will just plan on spending a little extra money on oil and keeping an extra fuel filter handy just in case.

Does this business about the injector seals sound logical??


The truck runs great and I do oil sampling at every PM. The samples come back good, however, I have heard Kevin say several times lately that adding that much oil they should. The only change I have noticed in the last few months, is that it smokes more (black) under a heavy load and during gear changes. That would be from the oil and other substances in the fuel, so I would expect that. In a way, this is a relief because I suspected internal problems. There is very little blowby and I could not imagine where all the oil was going. My main concern lately has been how to keep the injectors clean. Thanks again for the response.


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engine oil can mix with fuel at the high pressure fuel pump on an isx. with the high consumption and black fuel i would say theres a good chance thats your issue, also might have the injector travel set by a shop, its easy to run the overhead on an isx and can be another cause of black fuel because if the injector isnt closing all the way or at the right times then it can get a tiny amount of combustion into the chamber. ashpaltene is a product of the refining process for crude oil.

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It is possible to get crossing there, many will say it is not. And if you never shut it off they would be right, the fuel system is at a higher psi than the oil system while running, shut it off and the pressures become near equal, giving the opportunity to mix. The amount will be small, and an oil sample will show this problem, does the truck run okay? I would begin a regular schedule of sampling the oil and until you see a major issue on the horizon simply be aware of it. We have a few isx with dark not black fuel but no real issues so we keep running them. As far as a fuel cooler, find yourself another mechanic these things flow enough fuel to make you fall over, and you put a fuel cooler on in the north winter and you will need a bypass, the fuel will generally be below engine temp and that's about the best you can do

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Today I took some fuel from my fuel filter. It's Volvo D13 engine.

And I discovered that half of my filter contains oil. What could it be?

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Just had my international 9400i with Cummins isx serviced. It has 916xxx miles on it but a inframe was done about 250,000 miles ago has started smoking more and more and I've been watching the water separator and the fuel is looking very dark. When I took it in this time for service the mechanic said he thought my fuel was being contaminated with oil. Could it be I'm having same kind of injector problems.

How should I have this diagnosed. Is a overhead the way to go or is there a better way to find my problem

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tompetty69 will be eternally grateful.
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