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My question is specific to diesel or gasoline (petrol) engines.
Many people told me that it is very bad to run out of diesel since it can damage the engine and it's difficult to re-engage it afterwards.
Is it true? What would happen if I ran out of diesel? What parts would be damaged?
Some diesel engines will have problems, others will not. It all depends on how the injection system works on the vehicle. The bigger issue to worry about is the extraneous parts, such as the fuel pump (primary or low-pressure and secondary or high-pressure). Diesel is primarily an oil, which helps cool and lubricate the parts it comes in contact with. Those parts include the pumps (as mentioned) and the injectors. When you run out of fuel, parts tend to heat up, more-so the pumps than the injectors, because at least the primary pump will continue to try and pump with having the aide of the fuel to cool it. This is actually true of most in-tank fuel pumps used in fuel injected vehicles whether it's diesel or gasoline.
Bottom line is, don't run your fuel low, as you can be causing your fuel system issues. It probably won't hurt the engine itself, though.
Older diesel systems had to siphon fuel from the tank. If they ran out of fuel, it was heck trying to get them started again. You had to bleed the air from the system so it would siphon again. You shouldn't have to worry about this with newer vehicles (whether gas or diesel). Like I stated earlier, they use one pump, usually located in the tank to provide the fuel to the secondary pump, where it is pressurized to a much higher level. A lot of diesel vehicles also use more than one fuel filter to ensure the fuel going into the injection system is pretty clean. The tolerances on the secondary injection pumps are pretty tight, so foreign matter in there could reek havoc.
Nothing will be damaged if you run out of diesel, but the injector pumps don't work if there's even the smallest amount of air in them. Therefor it will be necessary to bleed the air completely from the fuel lines and injector pumps before the engine will start and run properly.
Regarding junk in the bottom of the tank getting into the system, that's what the fuel filter is for. There's usually a cheaper pre filter that will catch all the junk. If it's clogged, clean or replace it.
If the engine consumes all the diesel in the tank, it also consumes the dirt/leavings from the diesel that tend to accumulate at the bottom of the tank. The dirt will go into the engine and into the alimentation circuit and a clearing will be needed because dirt may hinder the circuit.
Also, if you run out of diesel there won't be any more in the circuit and it will have to be restarted (as in to make diesel go into the circuit again) manually or with a separate pump.
I had a blown gasket in my diesel engine fuel pump. The car would sometimes stall because I think air got into the system. Cranking the engine worked temporarily until I replaced the fuel pump.
Most autos and even heavy trucks suck fuel out through the top of the tank nowadays and the pipe doesn’t empty the tank completely the fuel filter will swell and collect most of the water which condenses unside the tank in cold weather this water will freeze and cut off fuel flow.
Airlocking used to be a problem 50 years ago most engine now recirculate a small amount bask to the tank this allows self bleeding of air out of the system.
JD tractors need the lift pump pumped as hard as it can be before they start easily. Some car may be the same but our BMW started easily after it ran dry showing 51 kilcks to empty.
Most will start after some cranking and it’s defiantly a good idea to change filters after running out of fuel.
Generally modern engine especially high pressure common rail pieso electric injectors will not start with less than around 12.4 volts at the computer.
