Why do some diesels require ether and some dont??

WF owner wrote: ...read your manual and follow the instructions for your particular engine.

YES YES YES!

And while diesel engines are all the same with respect to 'compression ignition'... they're not all the same with respect to HOW they accomplish it.

There's direct, and indirect injection... there's different concepts in head design, rod length to stroke ratios, and compression ratios... so they all have a little different character.

Starting a cold engine, regardless of WHAT type it is, is really one of the hardest events on an engine.  Oil is cold, oil pressure goes from nonexistent, to insane... the starting unit is under tremendous load to just TURN it, and trying to get it spinning FAST enough to bounce past TDC swiftly... the battery is cold... a little trace of moisture in the connections... cold air coming in...   accomplishing that pressure spike hot enough for compression ignition to occur ENOUGH to kick the flywheel hard enough to clear the next several compression events...  the fuel is cold... injection pump and injectors hate that.

Listen to how an old aircraft V12 or radial starts, and you'll notice that it doesn't all start at once... some cylinders hit, while the others are still missing... eventually they pick up, after they've spun a bit and cleared out whatever was fouling.

One of the first diesel-starting challenges I had, was the pony-motor 6cyl Cat mentioned above.  I don't know if they're ALL that way, but the one I worked on had a lever that opened up the valves, so that pony motor exhaust was blown through the cylinders to WARM them.  While it was doing that, it was circulating lubricating oil and coolant (both shared with the prime mover) to get both up in temperature for an easier start.  Spinning the engine for all that time seems silly, but in terms of long life and starting assurance, it's the right thing to do- they designed it that way, and that's one of the biggest advantages of a pony-motor start.  Unlike an electric starter, that pony motor could roll the engine over all day if you keep the starting fuel tank full.

On the locomotives I taught on, four 72vdc electric starting motors were wired up in series-parallel switching so that the crank could be rotated slowly to check for a flooded cylinder.  A leaking injector can put enough stray fuel in a combustion chamber to hydraulically prevent a piston from crossing TDC, and if forced, the cosine angle of crank against the rod can easily bend the rod and crank... so they have a programming sequence in the system to turn it slowly with the electric starter through four complete revolutions of the crank, after that, they bring it up to cranking speed, make sure they have oil pressure (it actually uses a booster pump for 20 seconds or so before cranking) then they tell the fuel management system to processed with fueling.  The fuel management system is full authority, and uses peizoelectric sensors on each head to detect when ignition occurs, and it watches each cylinder for misfires.  It brings on fuel to each cylinder individually, and adjusts it to get ignition, because each cylinder is slightly different, both in initial state, and in running character... so it's like having a mechanic assigned to each carbeurator of an individually carbeurated engine.  Once the engine is running, then it goes through a short warming cycle before it will allow running load (basic power generation), followed by a considerable warmup cycle before it will allow the prime moving load... all to make sure that million-dollar engine exceeds a 5 million-mile lifespan.

On a side note the Case forklift I posted about has a Cummins 4-390 engine in it. Now it does have a slight fuel leak at the fuel injection pump which the mechanic took a look at and said he could fix no problem. I also ordered up an owners manual for this machine. So with that said could a leak at the fuel pump have anything to do with the motor not wanting to start as easily?