Is it by experience or sound of the engine? Because that's what I'm told. I would like to know if there's any tips/tricks to differentiating between diesel and gasoline forklifts.
One has a diesel engine and therefor takes diesel fuel to run, the other is a gas engine and it will take gasoline to run. They will sound different and have different ways of start up, if your concerned look for spark plugs. Of course back in yesteryear there were machines that started on gas then would be switched over to diesel.
Is it always different in starting up method and the spark plugs?
They both have a similar starter motor so I don't know how that will help. Identifying the diesel injection pump, lines and injectors, instead of distributor, spark plug wires, and spark plugs will usually work. But some newer engines don't have a conventional distributor or injection pump, it's all hidden. Following the "throttle cable" to it's end is one good clue, on a gas engine it almost always goes to a governor which is connected to the throttle plate, or directly to the throttle plate, either in a carburetor or attached to the intake manifold that has gasoline fuel injectors, or propane mixing setup. The American diesels that started on gas were built more than 50 years ago so don't worry too much about seeing one of those in Jakarta. Nissan made a diesel with a throttle plate (injection pump was controlled by vacuum) and I know that engine was used in forklifts, but might have had a different setup in forklifts.
Thank you for the information, really appreciate it. Now I shall compare them side-by-side physically.