My bud runs a diesel generator with cooking oil. Biggest two problems...filtering and viscosity. The oil is dirty and really eats up filters. Also the oil is thick when cool and needs to be heated to something like 130 F to flow well enough. He runs the exhaust through a heat exchanger to preheat the tank. The initial start is done by heating the fuel with a electric heater. Once its running...its fine. Not really efficient in terms of work necessary, but its a novelty for him. He is in the business of instaling co-generation units ( electricity / heat ).