Running on Empty
May 25, 2007 3:33 AM   Subscribe

Running out of fuel: does it really harm a diesel engine?
posted by chuckdarwin to Travel & Transportation (9 answers total)
Not the engine per se, I don't think so. There are sometimes issues with injectors- you might have to bleed out the air that gets in the system. Aside from that about the only harm which could come to any of the mechanical underpinnings would be the trash in the fuel going up the line. All the same, if given the choice, keep it fueled.
posted by bkeene12 at 5:13 AM on May 25, 2007

Diesel fuel also acts as a lubricant and coolant for the high pressure fuel pump and fuel injectors in some engines. Since running out of fuel in those designs could cause expensive catastrophic damage to some parts, they generally have sensors to shut down the engine in situations where the tank fuel level drops below a certain minimum. How is that accomplished? By cutting off fuel flow to the injectors. :-)

That may sound like a contradiction, but a diesel that has its fuel supply cut off intentionally stops running smoothly and immediately. A diesel that suffers several seconds of intermittent fuel flow to various cylinders sputters, and can experience some very badly timed fuel burn cycles, leading to excessive pressures on pistons, connecting rods, and crank shaft components. In certain two stroke marine diesels designed to run in either direction for reversing propeller motion, such operation can even cause drive shaft damage if the engine unintentionally reverses underway.
posted by paulsc at 5:15 AM on May 25, 2007

Running out of fuel is so common that one would think some protection is built into cars to stop the car being written-off.
posted by humblepigeon at 5:31 AM on May 25, 2007

humblepigeons: In gas engines, it just stops running. The complication of diesel is the lubrication part that paulsc mentioned.
posted by mendel at 5:56 AM on May 25, 2007

Thanks, paulsc.
posted by chuckdarwin at 6:10 AM on May 25, 2007

Sideline to the posters question, would this also hold true for newer common rail diesels?
posted by acro at 8:06 AM on May 25, 2007

acro, for the Bosch style common rail systems of the last 10 years, I think that the system's EDC (Electronic Diesel Control) will shut down the engine on low fuel pressure, before there is engine damage. But running a diesel car that low on fuel isn't a good idea anyway, simply because there is inevitablya greater amount of dirt and contaminant in the bottom of the tank, and using the last few liters of usuable fuel capacity tends to plug up fuel filters faster than would happen if you filled the tank on a less aggressive schedule.
posted by paulsc at 12:09 PM on May 25, 2007

Thanks for the link, I'm a sucker for piezo tech: "In the 3rd generation of Common Rail for passenger cars, the injector actuators consist of several hundred thin piezo crystal wafers. Piezo crystals have the special characteristic of expanding rapidly when an electric field is applied to them. In a piezo inline injector, the actuator is built into the injector body very close to the jet needle. The movement of the piezo packet is transmitted friction-free, using no mechanical parts, to the rapidly switching jet needles."
posted by acro at 1:39 PM on May 25, 2007

Depends what kind of engine. On most tractors, if you run out of diesel you have to bleed the fuel line to get it started again. Not damage, but fucking irritating. Most people only do it once.
posted by unSane at 2:53 PM on May 25, 2007

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