I think I posted this once long ago, and the thread disappeared. 
Anyway, this is my question:
For the sake of argument, would it be possible for the driver of a vehicle with a diesel engine to use motor oil as fuel? Granted motor oil is more expensive than diesel oil, but in a pinch the occasional supply of Pennzoil or Havoline might suffice, perhaps, when the standard diesel fuel is unavailabe or at least distant.
Is this feasible?
I’d be interested to know as well. I think the main issue is going to be motor oil’s thickness as related to fractional distillation/flash point. I think filtered grease from a fryer may be a better candidate at first.
Here’s something…
Heck, I thought burning was what internal combustion engines were all about!
Somewhat anecdotal.
I run a Citroen C5 diesel and visit a site dedicated to such monsters. They are beset with quite a few problems mainly centred around the EMS computers.
One user (taxi driver) had some fuel related problem come up on the info screen and took his car to the dealer who estimated the repair to between £2700 and £3100 depending on the amount of replacement parts needed and the time taken to do it, central was replacing the fuel pump at £1000.
As the car was running reasonably well he deferred the work for a while. One of his taxi driver mates advised him to chuck a gallon of engine oil into the fuel tank then top up with diesel, which he did.
After driving 20 miles the fault advisory disappeared and never returned.
I fuel mine with biodiesel derived from recycled chipfat - well, cooking oil anyway.
As a result I have been looking at an Australian site devoted to biodiesel and its users.
A lot of the Australians use straight cooking oil.* They start up on standard diesel then switch to cooking oil once things have warmed up and also revert to standard diesel for the last few miles of their journey.
To do this they have to fit a conversion kit that is primarily a diverter valve to swap from diesel to Mazola, a second fuel tank and a heater to warm the cooking oil as it is too viscous to vapourise properly unless thinned somehow.
So it would appear that yes, it would work but not without being thinned somewhat.
I saw on Top Gear where they took an old Volvo and ran it on recovered filtered cooking oil that had had some turpentine substitute added to it and it went quite well. How well in the long run I couldn’t say as this method doesn’t remove some contaminants that over time would damage the fuel pump, soften seals and clog the injectors.
*there is no fuel tax on this in Australia, unlike here, where you would be prosecuted by the IRS if it was undeclared.
Probably not, and certainly not without some additional equipment. As a couple of people have noted, motor oil is much more viscous than diesel fuel. The viscosity is important for a couple of reasons.
First, when the fuel is injected into the cylinder, it needs to be sprayed in so that very small droplets are formed. When the engine is hot enough, the droplets evaporate to form a vapor, which then ignites under pressure and creates the force the makes the engine go. If the fuel is too viscous, it won’t form small droplets and so it won’t burn nearly as well.
The second reason that viscosity is important is more a effect of the fuel chemistry, as opposed to the physics of droplet formation. As hydrocarbon molecules get larger (longer, more cross-linked between the C and H atoms), the hydrocarbon goes from a gas (think methane, CH4) to a solid (think paraffin - wax). In between, you get some pretty thick liquids. The larger the molecule, the harder it is to break it down during the combustion process.
You could reduce the viscosity of motor oil by heating it up so that it would flow in a similar manner as diesel, but that would not address the combustion properties. It might be possible to run for a while if you had an oil heater (heating the oil to 200 or so deg F), but it would probably completely screw up your fuel injection system and probably would not run very well. I definitely would not try it.
There are very large diesel engines that operate using heavier fuels, but they tend to be slow-speed marine engines. These can definitely use motor oils, but they usually use stuff that’s even thicker and dirtier than motor oil.
The other thing that has to be taken into account is how well the fuel helps lubricate the engine. Since motor oil is designed to do that, lubrication would probably not be a problem. Biodiesel and vegetable oil may not do quite as well, which could cause some problems. Interestingly, sulfur tends to act as a pretty good lubricant, and when the standards for sulfur content in diesel fuel were lowered about a year ago, the refiners had to come up with additives to help keep engines lubricated. I think they’re doing similar things for biodiesel.
Slight hijack:
Back in the day, a buddy’s diesel truck ran out of fuel in the boonies. He siphoned (stole) some fuel from a construction site nearby. Turned out to be kerosene, but it got us home, about 30 miles. Smoked like hell all the way. Can’t remember any permanent damage to his engine.
End of hijack. Carry on.
I know of two cases where a mechanic overfilled the crankcase when doing an oil change on a diesel car.
in both cases the engine sucked the excess oil from the crankcase via the PCV system and the engine ran uncontrolled until the oil level dropped enough that the oil was no longer being sucked up.
In this case the word uncontrolled means at or above red line without any way to shut the engine off. :eek:
In both cases the amount of smoke generated was impressive to say the least. :eek: 
:eek:
Burning straight motor oil might work in older diesels, but I doubt it would in modern computer controlled engines. It would burn very dirty and carbon up the combustion chamber and the turbo, which is very expenve. There are many truckers, from about pre 1980, who would dump the crankcase oil, after a change, into the fuel tanks. I doubt there are many foolish enough to do this today. Some even believed that it helped the injectors, although I’m very skeptical of that claim.
Would a modern diesel run on motor oil in a real emergency? Maybe, I don’t really know, but Rudolph Diesel demonstrated that his engine would run on coal dust and many vehicles, in Europe during WWII, ran on wood smoke.
I’ve known ordinary gasoline engines to “diesel”–I’ve been present to see it happen. Obviously engines not even dsigned to use oil as fuel can do so, though I wouldn’t want them to get into the habit of it.
I have a cousin who once worked at the fuel dock on the pier in Redondo Beach, CA. Through some mistake, a customer had him fill the tank of his motorboat with gasoline when it should have been filled with diesel oil! The cousin’s boss found out and said, “Well, you’ll just have to empty the tank or this dock will go sky-high.” It took hours to get the gasoline out of that boat’s tank. :eek:
Dieseling happens in a carbureted gas engine because carbon deposits inside the cylinders heat up enough to act as a glow plug, firing off the fuel air mixture that enters through the manifold.
I guess that I could see how a worn out fuel injected engine could diesel because enough oil is making it past the rings, but I’d expect that the plugs would become oil fouled before this would happen.
There’s a funny story to this:
A few years ago, when this was new, a bunch of guys did a promotional trip around Australia in a specially converted diesel van. They would fill up by going to restaurants and takeaway food shops and asking them for their old oil (the proprietors were usually glad to get rid of it). The upshot of this was that they’d drive a few hundred miles stinking of fish and chips, then the next few hundred miles reeking of Chinese food, then fried chicken…
Remember the sitcom in 1975 On the Rocks in which a character named Fuentes peed into the gas tank of a prison van? I’ll bet THAT smelled!