Putting Crankcase Oil in Diesel Tank

[Artif]

Particulate matter shouldn't be a problem with used engine oil, unless you run your engine without fuel filters. You'll get more particulates from a steel fuel tank.
I believe Nordhavens have used oil feed systems built in to their boats from new.

[psneeld]

Well....some of us agree that we feel no need to add motor oil to our diesel fuel supply...but that's us.

Steve W's initial post of up to what amount of used oil may be harmful is a difficult question to answer. Some anecdotal and one study result.

Seems like small quantities in lower performance diesels have little or no effect. Exceeding a percent or two can start diluting the natural and required additive lubricity to newer ULSD and therefore may become a problem.

Using it to supplement fuel supply in enough quantity to reduce fuel costs could very well increase maintenance costs or replacement costs in the long run.

[doug86]

Originally Posted by psneeld

Using it to supplement fuel supply in enough quantity to reduce fuel costs could very well increase maintenance costs or replacement costs in the long run.

I don't think anyone was proposing that the practice would reduce fuel costs. It is more about reducing the hassle, and possible costs, of disposal.

[Dockhead]

Originally Posted by psneeld

Well....most of us agree that we feel no need to add motor oil to our diesel fuel supply...but that's us.

Steve W's initial post of up to what amount of used oil may be harmful is a difficult question to answer. Some anecdotal and one study result.

Seems like small quantities in lower performance diesels have little or no effect. Exceeding a percent or two can start diluting the natural and required additive lubricity to newer ULSD and therefore may become a problem.

Using it to supplement fuel supply in enough quantity to reduce fuel costs could very well increase maintenance costs or replacement costs in the long run.

The study did not find a "dilution of natural and required lubricity"; it found a small, statistically insignificant improvement.

I would do it if I were sure it did no harm. Why not consume it for fuel instead of throwing it away? 8 liters from an oil change is an hour to an hour and a half of running -- great!

But my main engine is turbocharged and intercooled and has high specific output -- I believe the tolerances are pretty close. I wouldn't risk it based on this amount of information. I don't buy the argument that the concentration is so low -- 0.5% is only one-half of the concentration of oil mix used in some modern two-strokes. God knows what waste substance in the oil might corrode or disturb the delicate injection pump or injectors.

But again -- if Yanmar officially stated that such and such a concentration of used oil is ok -- I would happily use it, saving the trouble of disposing of it, and getting a little bit of free fuel in the bargain!

[Artif]

Originally Posted by Dockhead

God knows what waste substance in the oil might corrode or disturb the delicate injection pump or injectors.

As opposed to the delicate interior of your engine which would corrode and wither away if you left the oil in the sump for months at a time

[YourOldNemesis]

Yep. Seems like a good idea to me. Those of you concerned about particulates getting into the injector pump - don't forget you've got filters for that. Those of you concerned about having combustion products in your fuel - don't forget that all the valves, pistons etc... are exposed to combustion products all the time anyway.

Many car diesel engines have exhaust-gas recirculation systems too - where the exhaust is circulated back into the air-intake - combustion products entering the engine!!

If you have a look at how your engine breathers are set up, it's highly likely there's an overflow from an oil-breather into the airbox (there is on most engines, including the one for my diesel car). When that breather goes 'glug' it's going to deposit a spoonful of oil in your air-intake for a couple of cycles, resulting in a lot more than the 1% concentration of oil in your fuel that you're getting worried about.

[Dockhead]

Originally Posted by Artif

As opposed to the delicate interior of your engine which would corrode and wither away if you left the oil in the sump for months at a time

Your oil pump, crankshaft bearings, big end bearings, wrist pins, pistons, rings, camshaft, camshaft bearings, and lifters are extremely blunt instruments compared to your injection pump.

The clearances in your main bearings might be a few thousandths of an inch. The clearances in your injection pump might be a few millionths of an inch. Your injector tips might have clearances of 1.5 microns. Don't compare the interior of your engine to the fuel system.

[YourOldNemesis]

Originally Posted by Dockhead

Your oil pump, crankshaft bearings, big end bearings, wrist pins, pistons, rings, camshaft, camshaft bearings, and lifters are extremely blunt instruments compared to your injection pump.

The clearances in your main bearings might be a few thousandths of an inch. The clearances in your injection pump might be a few millionths of an inch. Your injector tips might have clearances of 1.5 microns. Don't compare the interior of your engine to the fuel system.

FUEL FILTER

[Dockhead]

Originally Posted by YourOldNemesis

FUEL FILTER

The secondary (fine) fuel filter on my 4JH3HTE is a 10 micron. The primary Racor is a 30 micron. The injector tip clearance is only 1.5 microns. Any questions?

But I'm not sure that it is even particles which is the potential danger. What about the acids and other nasty chemicals which are produced in lube oil?

I'm not saying it's harmful to burn used lube oil in your fuel -- maybe it's not. I can well imagine that it is not harmful. But I ain't burning used motor oil in my fuel without clear and unambiguous information that it is NOT harmful. I don't possess such information.

[GordMay]

Originally Posted by Dockhead

... I ain't burning used motor oil in my fuel without clear and unambiguous information that it is NOT harmful. I don't possess such information.

Indeed.

[LostAtSea2011]

I know several old time truckers that have been doing this for years in their trucks but I would never do it....I don't like changing fuel filters.

[Artif]

Originally Posted by Dockhead

Your oil pump, crankshaft bearings, big end bearings, wrist pins, pistons, rings, camshaft, camshaft bearings, and lifters are extremely blunt instruments compared to your injection pump.

The clearances in your main bearings might be a few thousandths of an inch. The clearances in your injection pump might be a few millionths of an inch. Your injector tips might have clearances of 1.5 microns. Don't compare the interior of your engine to the fuel system.

I've been in engineering for quite a while, apprentice trained as marine engineer.
I've manual machined components to +/- 0.001mm i.e +/- 1 micron on prototype engines.
I currently work for a world leading hydraulic controls supplier, so I've got a pretty good handle on contamination and close tolerance work.

As you have already pointed out your fuel filter is only good for 10 microns, therefore your fuel system can cope quite well with 9 micron particles.
Personally I would use a 5 micron filter.
Most of the corrosive agents in your engine oil come from the fuel, which have already been through your fuel system. As already seen, some reports have mentioned reduced wear in engines running with old oil and fuel mixed.

ATEOTD it's your choice

[sww914]

My wife pointed out to me that in our family we don't eat our boogers. I haven't seen any studies that say that booger eating is harmful. I'm sure that some people have eaten their boogers successfully or even joyfully for many years. Boogers may even be nutritious. For all I know, they're delicious but I'm still not eating my boogers.

[thinwater]

ISO standards for marine diesel forbid mixing used oil. This resulted from many horror stories.

Trucking companies have their used oil collected. It was studied to death and found to be far more trouble than help.

Mostly it works... except when it is very expensive.

This horse has been researched, beaten to death, and carried off.

[SPARK]

Fuel additives are often up to 4 microns. That is why it is not recommended to filter smaller than 5 microns.

I can't comment on using used engine oil, but what do you do if on oil change is 20 liters and you are cruising in remote places. You have a choice of dumping (legally) on some island where the locals might or might not dispose of it properly, or carrying it with you to some civilized place with proper disposal facilities. This could be months.

On the other hand a lot of people here put 2 stroke oil in the diesel tanks of their pick-up's. About 1/200. I can say that it definitely makes the engine smoother and quieter.