Putting Crankcase Oil in Diesel Tank

[Steve W]

I've been asked to post this question: At what point would adding used crankcase oil to the diesel fuel tank begin to negatively affect the engine performance and reliabilty?

My boss owns a 44' Gulfstar trawler with twin 135HP 6 cylinder Perkins engines. He changes the oil twice a year and pours the (total from the semi-annual oil changes) 8 gallons of used crankcase oil into the 400 gallon diesel tanks. He burns 800 gallons/diesel/yr and refuels four times/yr, adding 200 gallons of diesel at each fill up. He has been doing this for 10 years, so has burned 8,000 gallons and added 80 gallons of used crankcase oil over that period. Boat burns 4/gal/hr at 9 knots cruise speed, engines start and run fine and burn about 1/2 quart of oil between changes. He is concerned that at some point the used oil to diesel ration will become high enough to begin causing problems. Any thoughts?

Thanks,

Steve

[Tellie]

No offense, I never understood why some sailors play games with very expensive equipment. Ask Perkins their opinion. I'm sure their answer is obvious.

[St. Elsewhere]

I would expect increased wear on the injectors, and it is a surprise that symptoms have not appeared before now.

[doug86]

If you pour the dirty oil into the fuel tanks, then either you will have to change your fuel filters more, or even risk introducing bad stuff into the injector pump. Used oil is dirty! It has soot and carbon and all manner of yuck in it.

Dirty fuel is perhaps the most common problem with marine diesel engines. Why would you want to add dirty oil to what was clean fuel?

[Bill Burgette]

I think it would depend on which diesel fuel he's purchasing. Sulfur lubricates injector pumps and injectors. The new fuels with 15 ppm sulfur instead of 500 or 5000 ppm do not lubricate as well and many truckers have experienced pump failures after switching to this new fuel.

The sell lubricity packages for older engines that re-introduce lubricating agents back into this new diesel. Since many of our boats have been designed to run on the old standard of fuel I would think that adding a little lubricating agent (used oil) would not be harmful and may, in fact, help.

I don't believe marine use diesel has to be this newer standard but with refineries required to produce 80% of the low sulfur fuel you may not know what's going into your tank. The fuel delivery service doesn't have to sell marinas low sulfur fuel but they can.

As was mentioned earlier, a call to your engine manufacturer with a question about ultra low sulfur fuel and your particular engine would be in order.

[Lowcountry]

I've heard of people putting small amounts of two stroke oil in their black iron fuel tanks to help with internal rust, but never putting used crank case oil in there. That doesn't make any sense to me.

[Duncho]

I agree with Tellie - check with Perkins. While not an engineer, I managed a small island electrical utility. Due to the cumbersome process of "re-exporting" our waste oil, we used it in our Cummins diesels. To do so, the engineers installed a mixer to deliver the waste oil at a specific ratio to diesel fuel. According to Cummins (in this case) the waste oil would improve lubricity in fuel for high speed diesel's.

However, check with the engine manufacturer. They usually have specific requirements for using waste oil, as well as modified maintenance procedures when doing so.

It is not a new concept, and is well understood by the manufacturers. Has been done in the power sector for decades.

[GordMay]

Greetings and welcome aboard the CF, Duncho.

[Steve W]

Thanks for the replies, I agree it makes no practical sense, but he has been doing it for 2,000 hours with no problems, probably because the tanks are so large, diluting the potentital issues. BTW, he is a 70 year old mechanical and electrical engineer, has been designing industrial machinery for 40+ years, has at least a dozen patents and relishes going against the grain. His current personal project: he bought a dead Bronco II, removed the body, restored the frame, installed a John Deer diesel with 9,000 hours on it and put a Land Cruiser body on it. Drove our shop workers nuts, but it looks great and is a blast to drive. A very talented guy with some interesting ideas and a lot of fun to work for. Part of my job as his national sales manager is keeping him from scaring the customers away with some of his ideas.

[Chief Engineer]

No Comment

[boatman61]

I've been known to put the chip (Fries) pan oil in my tank.... when I had an inboard....

[PamlicoTraveler]

A diesel engine can take a lot. I know one of the boatyards that uses the used fuel and diesel dump barrel for tractor fuel. Biggest enemy is water. I would never do it with a boat engine.

[boasun]

Diesel engines that use heavy diesel fuel, this were the used lube oil goes straight into the fuel tanks.
But am not sure on the diesels that use light diesel fuel as to whether you can get away with this or not. But on the work boats that use #2 diesel fuel, we always sent the used lube oil ashore to be recycled. The work boat engines cost several hundred thousand dollars each and we don't take any chances with them.

[psneeld]

probably no harm at those quantities...if he's had no problems after years of doing it...then the proof MAY be in the do'in....

You are talking 1% or so in quantity...I'm sure some of us have received poorer quality fuel at some point.

The likelyhood of something else causing serious engine damage is just as great in my opinion.

Do I recommend doing it? Heck no....I might burn the mix in a deisel heater...but I wouldn't do it to my engine because I don't have to or want to...but that's just me.

[ATC]

While I do not endorse it, you can add up to 5% used oil to the diesel fuel.

When we get in to an old salts fuel tank we can quickly tell where the used oil was going.