Adding used engine oil to the diesel tank

[Skillet]

Wondering if anybody has done this?  I have a fresh oil storage tank on my boat that holds my 15-40 (about 50 gallons worth), and am plumbing in a reversible gear pump to both drain and fill my engines and gear box directly from the storage tank.

I got to thinking, with every complete change I have about 10 gallons of used oil I need to store in 5gal buckets until I get to shore to dump in the WEO tanks.  Sometimes I have two changes
worth of oil knocking around down there before I get back to town. Dealing with those buckets is a PIA (empty or full) and dumping the oil always feels like I'm throwing money away.

My question is - what's the most % of filtered WEO you comfortably add to your fuel load?  I'll dilute it 50/50 with diesel then filter it through a 10 micron Racor before I pump it onto the tanks.  I carry about 270 gallons diesel in each of two tanks in my engine room, and will plan on those being at least half full when I add the oil to the fuel.  If they're fuller, that's a bonus. So adding 5 gallons to each half-full tank (135 gallons left in each) would give me about a 4% oil-to-diesel ratio.

Engine oil up here is about $18/gal.  If I can get $3.50/gal worth of fuel additive out of each gallon and not have to deal with dumping buckets after hauling them around for weeks I'll be stoked. Even with the costs of the extra fuel filters to pre-filter the
oil, not having to deal with the hassle of carting oil up the dock will be worth it.

Thoughts?

[Boss .300 winmag]

🤔

[Skillet]

🤔

Exactly! 

[meatwhack]

I know guys that have ran it in their Cummins pretty rich. I can’t remember the exact ratio but I think it was 50/50 or maybe even a bit richer. With the ratios your talking I don’t think you’d even notice it was there.

[Boss .300 winmag]

I know guys that have ran it in their Cummins pretty rich. I can’t remember the exact ratio but I think it was 50/50 or maybe even a bit richer. With the ratios your talking I don’t think you’d even notice it was there.

Maybe out the stacks.🤣

[Skillet]

I know guys that have ran it in their Cummins pretty rich. I can’t remember the exact ratio but I think it was 50/50 or maybe even a bit richer. With the ratios your talking I don’t think you’d even notice it was there.

Maybe out the stacks.🤣

Exactly what I thought! 50/50 seems like they'd be pushing some serious soot?  I'd probably not see much additional soot at 4%, correct?

[Boss .300 winmag]

Is there any non combustible additives in your engine oil?

[Skillet]

Not sure. When I buy engine oil in bulk, I get Chevron Delo 400.  I probably should check out the additive package.

[jmscon]

I don’t think you’d have any issue with that ratio. It will probably help lube the upper cylinder and make your engine last a little longer.

Do you have any finer filters in your fuel system?

[Skillet]

Yep.  10 micron Racor fuel/water filter out of the tanks to:

The main engine 5 micron fuel/water separator, then dual 2 micron filters before the injection pump.

The generator (Isuzu 4LE1) as another 10 micron fuel filter before the fuel rail.

[jmscon]

There ya go!
Might have to up the frequency of filter changes by a little bit just because it’s used oil.

[Special T]

I have done a fair bit of research on this issue..  on a mechanical injection  rig like yours it will work, but it comes at a cost.

You diesels are very dirty and you would need to filter much smaller than 10 microns. Napa makes a common fuel filter that is 2 micron. I run a 10 then 2 micron on my dodge and I dont use oil. The carbon and soot in the oil will eat at your  injectors.  That said I've talked with a guy that put 150k on a ford 7.3 that ran on a blend of 70% oil 30% gasoline.

Besides filtering the oil heating and settling the solids out are your best bet.

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[Skillet]

Interesting.  I just put a new pump and injectors on the main, don't want to shorten the lifespan on those.  I've got 2 micron before the pump, so it's probably safe.  But I've only got 10 micron (2 times) before my generator engine.

[Special T]

Those guys that are running a lot of motor oil have a centrifuge  which gets sub micron particles out.
For the guy with a 4x4 or military rig with a multi fuel mix is great. Mix may not be all that great with a. Boat

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[Skillet]

I have one in the gear locker, but it is kind of a bad design in that it leaked out of the bottom due to a porous casting where the oring seals up to the outlet hose.  I could have a machine shop fix it for me though.