I got the 4x4 on economical grounds, do a bit of caravanning, the wife wouldn't let me get it unless i could do it for next to nothing. 2500 litres rougly equates to 48 litres a week. I use roughly 25 litres if i am lucky, you do though have to be registered with sepa for the uplift and transporation of waste vegetable oils. The reason I decided to go for waste was because i am getting it for free. I don't use a preheater as they draw the amps out the battery. I use a heat exchanger, when i do a filter service. I half fill the fuel filter with redex and diesel, this cleans the pump and everything out on the 50/50 side. The Nissan terrano has the best type of engine for running veg oil, used or unused, as it has an indirect injection engine and combustion takes place in the cylinder head vortex chamber. Thus reducing the risk of any unburnt fuel to cause coke and also wear and tear on the engine. I researched this tons before i decided to take the plunge. I do oil changes but it usually on a 5 month basis. The build up of veg oil in the sump occurs mostly in direct injection engines, as the injector is directly above the piston head. If the fuel is not sprayed and heated properly this causes coke which wears away the piston rings, allowing the sump oil to rise.