Bleeding diesels

irule, May 21, 4:51pm
Can someone basically explain why you have to bleed diesels after you change a fuel filter or run out of gas or stuff around with the fuel system, yeah I know air in the system blah blah blah.
thunderbolt, May 21, 4:52pm
You answered your own question.

No fuel at the injector, equals no spray of diesel into the cylinder which equals no go.
ashwattau, May 21, 4:56pm
What I want to know is how you managed to run it out of gas.
budgel, May 21, 5:08pm
You end up with air in the system which is difficult if not impossible to remove by cranking the engine. You run a good chance of flattening your battery before it gets through,if it ever does.
mugenb20b, May 21, 5:12pm
If you don't bleed them, you'll most likely flatten the battery by cranking the starter motor for ever and ever. Although, in some cases the primer pumps are totally f.ed and you have no choice but keep cranking them or prefill the filters (which is not really a good idea). A lot of late model common rail diesel vehicles have no primer pumps anyway, so just fill up the tank, and follow manufacturer's procedures on how to start them.
brapbraprx7, May 21, 8:15pm
You have to bleed them so you dont f**k the glow plugs
for_an_angel, Mar 17, 12:58pm
Don't know how glow plugs work then!

OP
Any diesel engine with a rotary type injector pump or common rail will self bleed because they have a great return line but as others have pointed out the battery may suffer. The old in line diesel pumps had to be bleed the get the engine going. Why ! heres why the injectors open when the fluid pressure delivered from the pump over comes the spring pressure inside the injector. Fluid dosn't compress very well so you only need a small amount delivered from the pump to over come the spring pressure.
Now air can be compressed very easy so when it is stuck in the line between the pump and injector the spring pressure is not over come so the air sits there compressing and uncompressing and the injector never opens.