If you plan on running SVO (straight vege oil) then there are modifications that are need to be made to the fuel system. Yes it must be preheated and the engine warm before switching from fosil (used at start up and shutdown of the engine) to SVO. after you have driven for a while switch to svo then drive a bit further 5 minutes before you turn off your car switch back to fossil. As SVO with become thicker as it cools something you don't want happening in the engine. From all I have read people only tend to run this system in older diesel engines(heaps of info can be found about the old Mec engine running to fuel delivery systems.)
The common system or method is to turn SVO into biodiesel.
Mix vegetable oil (used or unused) with methanol (an industrial solvent) and sodium hydroxide (caustic soda) in a large mixing tank for 9 hours.A couple of days later a thin layer of black glycerol will settle out at the bottom of the tank. Draw off this glycerol to leave a clear amber liquid – biodiesel. You have to wash this biodiesel with water, which involves adding water, mixing again and then waiting for the water to settle to the bottom. Once you've drawn off this water the biodiesel is ready for use in any diesel car – no conversion required. - This has been taken form this
Site.
I am in the process of looking into, and taking my first baby steps and I hope in the next month to be producing my own Biodiesel. I am still very nervous about things such as fuel filter and pump and injectors as I have read that this is where problems can occur. If when I test the consistency of the home made fuel to normal diesel there is a considerable difference then I may re-evaluate my decision to go down this path. I may only run a mix of bio and fossil. A TD5 is a hell of an expensive test engine and that is why I say baby steps.
Adam
