Engine Oil in Fuel. How?

[Play'N Hooky Too]

Short Version: I'm wondering how it might be possible that I wound up with engine oil in my diesel fuel. (Detroit 8V71TI Engines)

Long Version: A couple of weeks ago we decided to head out for a day trip of fishing. The 46C has three tanks, the two mains under the cockpit that hold 200 gallons each and the mid tank that holds 250. A few years ago we filled up all three but since most of our trips since that time have only been for a day or maybe an overnighter, we never touched the mid tank and have just been running on the two mains and refilling those. So with diesel being close to $6, the two mains being down to less than half, and our planned trip being only for a short day, we thought it was time to use up some of that mid tank reserve.

We started out on the mains and about half-way to the pass we switched the fuel valves over to draw from the mid tank. After about a minute the engines began to push out some thick smoke, began missing and died. (Oh crap!) We switched back to the mains and restarted the engines with no problem. Tried switching them again at idle and got the same result. Without enough fuel in the mains to last us for the day we aborted and went back to the marina.

I got my fuel wagon, bit the bullet, and went to the local fuel farm for a load of diesel. We pumped that into the main tanks and resumed our trip the next morning. We had an uneventful trip, everything ran fine, filled the fish box with some nice yellow edge grouper and tile fish. On the way back in I noticed that we were getting some soot on the transom and the surfaces at the rear of the cockpit. By the time we got back to the marina the transom had a pretty heavy coating of soot. We never really saw any smoke from the engines, although the exhaust smell was a little more noticeable than usual in the cockpit at times. I suspected that we had probably sucked some nasty crap out of the mid tank when we attempted to switch over during our aborted trip.

Back at the dock I checked the Racors and they were completely opaque. I drained them and replaced the filters. The previous owner had installed a transfer pump in the engine room to pump fuel from the mid tank. Using that I pulled a jar of fuel out of the mid tank to see if it looked cruddy. It was clear but had more of an orange color than the typical bright red of off-road diesel. I suspected that we had likely mixed in some regular green diesel at some point, which would account for the color, but otherwise the fuel looked fine. I have a small dedicated fuel pump installed in the engine room that I use to refill the Racors and prime the engines after I change the primary filter elements. It pulls from the port main fuel tank. When I began refilling the Racors I noticed that they were completely opaque again!? I pumped about a gallon of fuel out into a jug and it was very dark almost completely black. Fuel from the starboard main tank was the same way.

At this point we began investigating to see what was going on. We found that all of the hoses from the mid tank had been removed, the pick-up ports and return lines had been capped off at the tank (except for the one attached to the transfer pump) and the connections for the feed and return lines at the fuel valve gallery had also been capped off. The only way to get fuel out of the mid tank is to manually pump it out using the transfer pump the previous owner(s) installed in the engine room. So essentially, when I switched the valves over to draw from the mid tank during our aborted trip, it dead-headed the fuel systems for both engines.

Below is a picture of my fuels. To rule out the possibility that we gotten a bad load of fuel, I pumped some of the residual fuel out of my fuel trailer. That's it on the right. The center jar is the fuel from the mid tank and the one on the left is the fuel from the port main tank. The starboard tank is the pretty much the same. There is about 75 to 100 gallons of this left in each of the two main tanks.

20220726_192838.jpg

The engines don't seem to have any issues running on the "dark fuel" (other than the soot). I pulled the dipsticks on both engines. The oil level is right were it usually is after running them for about 10 hours and the consistency is dark and oily, just like it is when it needs to be changed soon.

So the question is, how did I wind up with engine oil in my diesel?

Thoughts?

Thanks
-Alan

[Fanfare]

Many years ago (1970) I put in a "rebuilt" 12kw Onan generator which turned out not to have been rebuilt at all. Not only did it smoke so much that it was apparent the boatyard must never have tested it but it also ended up contaminating my forward fuel tank with black engine oil. This forward tank was the only source and return for the generator's diesel. Aft tank was fine. After a considerable hassle with the yard we replaced it with a new Onan so I don't know exactly what the problem was but the only cross-over connection I could think of was the rubber diaphragm in the Onan generator fuel pump which may have developed a crack. That pump was at the bottom of the crankcase so was exposed to splashed oil. In addition to the incredible exhaust smoke the genny was down a quart of lube oil daily. Obviously this oil was going somewhere. The yard accused me of getting contaminated fuel but oil analysis of each tank proved otherwise. Possibly this happened with your boat. I doubt it was just the age of the fuel. Back then it was not easy to dispose of 200+ gallons of contaminated diesel. And it was only 19 cents a gallon then!

[cenger]

It looks to me like the bottle on the left is home heating oil. Home heating oil has a much higher sulfer content. Not great to run in a DD but people do it to save money.

[Play'N Hooky Too]

Down here in south Alabama and NW Florida we don't get a lot of call for home heating oil. Not saying it is exactly the same as ultra low sulfur diesel for highway use, but it is billed as "off-road diesel" (ie: untaxed). They dye it red to keep people from using it in their vehicles and I have on more than one occasion seen Weights and Measures pulling samples out of people's tanks at checkpoints along the rural highways here.

Regardless, the diesel on the left is the one I'm concerned about.

[Captain Ralph]

If the tank was disconnected, Was this an old oil storage cell?

There is no way a Detroit is going to release engine oil into the fuel.
NO WAY.

[Play'N Hooky Too]

Captain Ralph, I didn't know if it might be possible for oil to be drawn in around the seals in the cam-driven fuel pump (?).

It had been suggested when I posted this on the Boatdiesel forum that it was algae in the tanks. But this has not been a problem in the past and especially not for both tank simultaneously. Not to mention there was no significant sediment in the Racors and whatever is causing the discoloration is not affected by passing through the Racors or primary fuel filters. Engine oil is the only other thing I could think of that would get into the tanks in sufficient quantities to cause the discoloration of 300 gallons of diesel.

I'm stumped.

[Captain Ralph]

8V71s have a direct drive, star gear fuel pump mounted on the front of the blower. The fuel chamber has a shaft seal then the shaft is exposed. The drive end from the blower has its own seal.
There is no connection.

Old commercial boats used to burn old motor oil under way. 5 to 10% to fuel.
Got rid of old oil quickly.

Also some remote or long range cruisers just kept old oil till they could pump it out at a place that could take it in bulk.

I take it this may be a new to you boat? Can you ask the previous owner?

Detroits will run on motor oil, banana oil, peanut oil, cheap cooking oil, lard, kerosene, JP, Saki and more. Refined diesel just runs cleaner and does not stink like a land fill or McDonalds.

[Play'N Hooky Too]

I've had the boat for about 6 years, but everyday is a new discovery concerning something that the previous owner did. Unfortunately, at this point I can't ask him anything unless I'm using a Ouija board.

The fact that the mid tank was isolated only became evident to me recently because, after working through some other issues related to it having sat up for a few years, we were finally getting comfortable enough to consider taking it out on some extended trips were the capacity of the mid tank would be needed. Not sure why the mid tank was isolated, but I presume it was for a good reason. Regardless, the fuel in it seems to be good and never entered into the issue at hand because we never drew from it during any of our trips, including this last one when I noticed the dark fuel in the main tanks.

Any thoughts on the fringe theory proposed by one of the dock-side diesel "experts" that the dark fuel could be the result of a faulty injector(s) letting exhaust gases feed back through to the fuel system? The expert once knew a guy that worked on a truck that was having this problem. Not really sure how this could happen with a 2-stroke engine.

Thanks
-Alan

[Captain Ralph]

I caution you listening to experts on the dock with a friend....

Send the dark oil to a lab.

[Play'N Hooky Too]

Any recommendations on a lab?