My 70's model D3 has a little starting issue. It doesn't like to start without pre-heat, even when it's 75 degrees out, and then it just barely starts, acts like it ran out of fuel. Once it's going, it runs like a top. It starts fine when it's warm too. I've pumped the priming pump and it doesn't seem to do anything. Any ideas?
Not knowing the current status of your engine I am assuming that it has not been rebuilt. If this is the case and it has a lot of hours on it, my guess would be that you don't have the compression it once had. Since the diesel engine uses heat to ignite the fuel, this is probably the case. May just be a case of old age I just rebuilt my D3 and she fires right up and I don't have glow plugs. Don't know how it will do in the winter but may just find out this winter. My 955 needs preheating to fire up easy, otherwise it will take a bit more cranking.
It might be getting tired. You could try a valve set and check the timing. Sometimes a little advance on timing helps if the compression is low.