Used motor oil as diesel fuel questions

Jan 3, 2020
Brittany 🇫🇷
With the fuel prices being so high, i was thinking about experimenting with other fuels, WVO being the main one. Since i always have a lot of used engine oil from the vehicles i service, i was thinking about burning it in my diesels. The blend would be something like 5 to 10% oil. The only concern is that my cars have catalytic converters. I'm not sure how different is a catalytic converter in a diesel compared to a gas car... Should i stick to WVO only as a alternative fuel?
I wouldn't put motor oil in my diesel's tank.
If you have an indirect NA 6.9/7.3 ford and don’t mind removing and cleaning injectors and replacing fuel filters often go for it.

It’s generally advisable to heat and centrifuge the oil first just like making biodiesel.

Also advisable to make a jacketed fuel line and keep the tank/fuel lines heated.

That said why not make diesel fuel for $0.99 a gallon instead
Just need an unlimited supply of plastic bags or #2,4,5,6 plastics need not be clean but no #1 or 3 plastics, a child can make the “reactor “

Overseas people have been doing it for decades, plans exist various places, Japan used to sell a countertop appliance, a Blest machine for consumer use.

You can't just dump used oil in. You have to filter it first. By the time you buy the proper stuff to filter it you are better off just using diesel. Any contaminants in used oil can cost $1000's in repair bills.
If you have a HPCR I’d steer clear of using used oil. If you have an older diesel then up to you. I’d make sure you clean the oil really good. There’s some YouTube videos out there about black diesel.

Just my $0.02
I did that sometimes in my old indirect injected diesel, approx 5L per tank (70L) when I had some used oil to dispose off.
Not sure if it had some adverse effect on the catalyst converter or not.
These guys specifically sell centrifuges for cleaning motor oil and tell you how to run It in cars or trucks. Though I've never done it myself.

Antique oil burners are about the best way to use up used unfiltered motor oil.

My grandfather even made a oil drip that he could turn on for his wood/coal burner to supplement and extend the burn, white hot coals make a good wick and nothing to contaminate

As for “black diesel “ that is not filtered motor oil, it is more difficult to make than plastic diesel but is made in a similar way where you heat WMO up to a high temp to crack it then use a sill to condense what you want similar to making everclear.
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I am currently running a 30% blend of filtered WMO. Still deciding on what kind of filtration setup will work the best and if i need a centrifuge or not.
What is your cost savings per liter of fuel?

What will it cost you to replace your pump and injectors when you ruin them?

Figure those numbers out and start the clock - let us know which happens first: fuel saving or huge repair bill.

And you will ruin this poor Mercedes. Just a question of: did you save much in fuel before it happens.
Bad move with super high pressure diesel fuel injection systems. And the additives in the motor oil will kill your catalyst and DPF.

Maybe OK if the diesel engine was the size used to power a container ship.

Worth taking a look at this YT channel. I filter the oil down to 1 µm. By the way i am just experimenting a bit. The car is a beater and i got it for a few hundred euros. I can rebuild the injectors myself it they fail, already did in the past. With multiple passes at around 1 micron i highly doubt it will harm anything running one 30% tank and a 5 or 10% blend here and there. I'll continue looking for sources of WVO, this is what i intend to run long term at 50% ratio. Keep in mind that one tank of diesel is around 120€ here. Three tanks of free fuel and i can rebuild the whole injection system and still not loose money.
Be careful with WVO. It’s got contaminants and can thicken easily in moderately cool temperatures. Enough to cause engine failure when it’s too thick to pump.

WVO systems usually use a heated tank and solenoids to switch the engine over from WVO to diesel for starting and purging before shutdown to avoid this problem.

Alternatively, you can treat the WVO to create (gross oversimplification, you’ll need a lot of equipment and filtration) actual biodiesel.
I know somebody who tried this with a VW 1.9 VE TDI and it killed the injection pump. I warned him but he learned the hard way.

In order for it to work you’re gonna need to centrifuge the WMO then filter with a benchtop polishing set up.
I used to run a Peuegeot 406 with an indirect turbocharged diesel engine. I was a student at the time and I used to run the engine on WVO, and always put a few litres of used engine oil in the tank. Never had any issues with it at all! It was actually smoother and quieter than when running on diesel!

I did used to change the oil every 3,000miles though because I'd heard horror stories about the WVO turning the oil into jelly.
In fact my biggest concern is from the environnemental point of view. I'd like to know what you think. I've received a few hateful messages on a WVO french forum after writting about experimenting a bit with waste motor oil/hydraulic fluid as a fuel. I do everything i can to minimize my impact in this world (including driving as little as i can, driving is my addiciton...). One side of me tells me that running a % of waste oil is a terrible idea while the other tells me that every other way of getting rid of the waste oils will probably have a worse impact. I'm not sure what waste oil becomes. Burned in big ships? Recycled into someting else? Either way, if i burn my own waste oil in my tank, i feel that it will have a lesser environnemental impact, less transport, less processing etc.