Burning used motor oil in an older diesel engine...?

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Mar 19, 2005
Greetings Friends - I just "found" this site, and look forward to sharing and contributing information.

I am considering burning my used motor oil in with the fuel of an older diesel car that I own (an 1982 Mercedes 240D).

I recognize that doing this with a newer diesel engine would be ill advised, but what about in an older engine...?

My thoughts are to filter the old oil first, and then to use no more than about 1 gallon per 17 gallon tank of diesel fuel.

What is the wisdom of this forum in regards to my plan?

Is there a readily available filter media that I could use (ie, coffee filters or similar)?

Thanks for constructive input
you could probably burn more like 1 quart per gallon and not notice any difference. however if it is 1 gallon or 17 gallons you will be polluting the enviroment more than compared to using straight diesel. on the other hand alot of used oil is just burned as fuel in big ships anyways so its i guess it doesnt matter in the end.

do what you want. them old benzes will run on amlost anything and last forever.
Seems like a high percentage of motor oil in the diesel fuel.

If you insist on doing this, I would start out at about a quart per tankfull. And before I poured it in, in addition to the filtering, I would mix the quart in with a gallon or two of diesel fuel in a container, and then pour that into the tank, so as to get better diffusion of that motor oil.

I have often been curious about doing this in my old 300SD, but have always thought better of it. Be sure to report back your results if you do it, specifically regarding smoke, odor, driveability, etc.
Id do just what k1xv said. I know others in the MB diesel circles that do this. The sulfated ash content can be an issue, so keep levels low.

That sounds like great advice.

I'll start out by using a smaller amount of filtered used oil (like roughly a quart) per tankful of diesel to begin with.

I'll also post back here periodically on the results.

I will also perform an oil analysis so as to establish a "baseline" on the engine, and perhaps as time passes I can ascertain if any harm comes to the engine through this practice (although I seriously doubt if doing this will harm my engine at all. I wouldn't consider it otherwise).

Any thoughts regarding filtration media? Sure, the engine oil is filtered to begin with, but I want to make sure I get everything out that I reasonably can expect to. How big is a soot "particle"? Can soot be filtered out, or is it not a major concern?

- Patrick
Ultimately its your injection pump and injectors... Injection pump 'damage' or accelerated wear won't necessarily turn up on a UOA.

Seriously though, a common method of used oil disposal in some big-rig maintenance shops has been to blend it with the diesel fuel supply.

Some diesel trucks sold these days even will inject a small quantity of motor oil at periodic intervals into the diesel fuel, to create some 'consumption' so that the driver will top the sump up with new additive-containing oil.
i cant imagine there being much injection pump or injector damage. i read some paper years ago that said bosch pumps and injectors need a 7 micron absolute fuel filter in order to filter out damaging particles. this was a paper published by bosch too.

guess what absolute micron rating youre fuel filter happens to be if you are using the correct one?
hint: its between 6 and 8.
the inline injection pumps wont see any damage. Some of the older ones were actually lubricated with oil.

If you get coking on your injectors, that is asking for trouble... thats why you need to keep it well diluted.

You might also think about adding an injector cleaner to your fuel, or skipping a tank or two every so often and using a good dose of rotella DFA or redline diesel catalyst to keep things clean.

Typically you need to run that 240 pretty hard, since youre moving a brick with 61 hp at highway speeds... so the high throttle and 'lots' of power will also actually help keep the operation clean and clear.

I burn my used oil in my '82 Kubota diesel at about a 50/50 mix and some Power Service. I sometimes add about a gallon plus some Power Service to a tank in my 2000 F250 7.3L Powerstroke if I haven't been using the Kubota much. The engines seem to run the same with or without the used oil.
This sounds very interesting. I have a '65 Case model 730 tractor and a 530 tractor. Both run on diesel fuel. Have you noticed any clogging of filters, greater smoking, increased fuel consumption - anything different at all?
Doesn't the trace materials listed in uoa's end up on your rings and cylinder walls after burning? Precipitate?
I've been burning my waste oil in my '93 Cummins powered Dodge for about 6 months. Cummins says up to 5% by volume is OK, more will cause injector coking. This goes only for engines not equipped with a catalytic converter. I'm running it as free injector pump lube, so I run a gallon per 30 gallon tank of fuel. That's about half the maximum Cummins suggests.

I have noticed no effects from this. Smoke is unaffected, power has not suffered, diesel fuel economy is up (takes one gallon less to fill the tank, no significant change other than that), and it hasn't plugged the filter. Out of curiosity I cut the fuel filter open the last time I changed it. The media was black from the soot, but there was no sign of large particles. I dragged my fingernail across the surface of the media to see if there was soot/sludge buildup on the surface of the media, but I didn't find any. The truck made 345 HP/863 ft# on the dyno the week before the filter change, so I don't think the filter was restricted.

I would not expect smoke problems unless you exceed the 5% allowance by a lot. This is because the oil is actually burned in the cylinder as opposed to being consumed due to poor ring seal or a bad valve guide. Oil mixed in the fuel is introduced at the right time for complete combustion. A worn out engine has oil coming in all the time and is not really burning most of it, just vaporizing it and passing it out the tailpipe.
We have some trucks that have an oil replenish system that meters crankcase oil in the fuel. These are 16 cylinder engines rated at 2300 hp. The oil rate can be adjusted from 0.25 to 0.75 percent oil to fuel. Fuel consumption is about 35 gallons per hour so it's not hard to figure out how much oil it uses. Today I visited with out mine product support manager about the system and he and I both have reservations about mixing oil in fuel. On the big trucks the oil is filtered through a 2 micron filter before being mixed with the fuel, also it hot oil so it will mix very easily.

If you want to mix oil anyway you might consider treating it like mixed gas for a weedeater - that is mix perhaps 1/2 gallon oil with about 5 gallons diesel in a separate can and shake the heck out of it. To be on the safe side let it settle overnight and then transfer to the vehicle tank without upending it, then top off the tank. The heavier solids will settle out and remain in the bottom of the can so not too many solids should be present. Make sure you are using good fuel filter, preferably 2 micron.

Good luck.

PS - as for the metals in the used oil causing problem with the rings, they are already exposed to used oil since they are lubricated with oil in the crankcase.
Given that:
* the "acceptable oil useage" given by a lot of manufacturers (for petrol engines even) appears to be 1 litre/1600km;
* the oil that these engines are ingesting is in all the bad spots (i.e. right at the extreme edges of the combustion chamber); and
* the oil that you mix will be fairly evenly distibuted through the chamber.

I'd say 1 litre/1600km (say half a litre per tankful) would do nothing really, and maybe double that would be OK.
I wonder if I could go down to the US and fill my car to the brim with new Golden State SA oil. It is cheaper than diesel and cleaner than used oil.
Anybody got research about this sort of thing?

Thanks, Steve
the guys who run Waste Vegetable oils go to great pains to get the viscosity down to the right level by heating whatever. (Some even cut it with regular gas).

Diesel is supposed to be about 3cst (@40C). You'll need to adjust that.

But I think straight engine oil would have too much additive.
The Golden State SA (yep, SA not SL or whatever is current) oil isn't supposed to have much additives if any. I've never seen it in Canada so I'd have to travel atleast 600 km to get the stuff and put in a under-hood heated tank so I'm not going to try it any time soon. I suspect used cooking oil has "additives" that can't be filtered out either.

I know a guy who is putting together an electronic control system to run WVO and biodiesel with no driver input. Once this is available I will consider making the jump. http://www.vocontrol.com/

I've burned motor oil and ATF in my 1991 VW Jetta 1.6D before. 1 quart per 14.5 gallon tank. Didn't notice any change at all as far as driveability.

Lots of people use ATF and 2-stroke oils in their older diesel engines to help lubricate the pump.
One crude filtering method that has been used for years is to use cotton or hemp rope as a siphon. Someone here suggested this a while back and since then I have heard of it from others also.

For instance, place a gallon of used oil in a gallon milk container. Put a fairly large rope in the oil and run it down to another container. The result is very clean oil with nearly no effort. It is my understanding that the cotton fibers do a fantastic job of filtering the oil.

I reported a long time ago that my oil was climbing the rope (cotton).

It got to around 18 inches in a couple weeks...and has been sitting there for months.

I'm going to try hemp (rope) next.
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