Does it have a Stanadyne/Roosamaster rotary injection pump? If so, that is a typical problem when the head & rotor assembly is worn inside the pump. Starts good cold, runs good cold and hot, but will not start hot. Easy test is just do this. When hot, turn it off. Then pour cool water over the pump. Then try to start. If it then starts right up, that is the problem. Do NOT pour cold water on the hot pump when the engine is running - make sure it is off.I have an 1855 Oliver Diesel that recently had an in frame overhaul. It starts great when cold and runs good but once it gets warmed up good if you shut it off it will not start again for about an hour, then it starts fine. Had the starter rebuilt and it turns over plenty fast to start. Anyone have any ideas what the problem might be??? Thanks for any help.
This is a common problem in Iraq on military Humvees that also use Standyne/Roosamaster pumps.
There are sometimes work-arounds if you don't want to spend money on the pump. Get it turning over even faster, and maybe try turning up the fuel delivery. The problem is, when the pump gets worn, and it is hot, the metal expands a bit, and the fuel thins a bit - all enough so at cranking speed it won't make enough pressure to crack the injectors. So, putting in more battery power can make it crank faster and might be enough to make a difference. Check voltage right now when cranking. It should be around 9 to 9 1/2 volts. If you increase battery size and get cranking voltage up to 10 or 10 1/2 volts, it can make a huge difference.
Also, to turn up fuel, you reach in the top with a hex Allen wrench and turn clockwise. 1/8 of a turn can sometimes make a night-and-day difference. How is the fuel setting now? Does it push any black smoke when you really lug it down?