updated March 3rd, 2008
There is alot of information on the web about running a diesel engine on SVO (straight vegetable oil) / WVO (waste vegetable oil). I am not an expert, as I have only been at this for about 20 months. Different car / kit combos require diffent applications and I can only speak of my TDI/modified Plantdrive experience specifically and other Vegetable oil conversions generally. The point of this site is education, to share my experiences and make people aware that vegetable oil as fuel is a viable option that is better for the planet & can be a low cost fuel alternative.
First, SVO is not biodiesel. Biodiesel is vegetable oil that has been chemically & thermally process to reduce it's viscosity. It can be used instead of diesel or mixed with it in a diesel engine w/o major modifications. In a VO car the viscosity of SVO is reduced using heat from the engine (via the coolant liquid) and/or electrical heater element. In most VO situations the engine is started & shut down on diesel - this requires 2 tank system. Some Mercedes Benz from the 80's & early 90's can function on a 1 tank system(VO only)
My particular set up is on a 2002 VW Jetta TDI (Diesel) with a 2 tank system. The kit I chose (and extensively modified - ie; this blog) is from a company called Plantdrive.com. In my situation in Southern California (a mild climate), I start the Jetta on Diesel, drive until the car reaches operating temperature(190† - as indicated by the water temp gauge), this can be anywhere from 10 - 20 minutes depending on the outside temperature, then I switch to Veggie. When I'm going to shut down the car for an extended period I switch back to diesel for about minute to flush ("purge") the veggie oil from the system. As you can see, for really short drives - 5-10 minutes - I would never switch to VO, instead staying on diesel. So the car is not 100% Vegetable oil. The longer my drives, the more I'm on Veggie and the more money I save.
Some kits do offer what I would call a semi-automatic feature (specificaly FryBrid's conversion). The car will switch over to vegetable oil automatically via a computer sensing the correct fuel/engine temp. However the purge cycle is still manual, as the computer doesn't know when you plan on shutting down . The benefit is there is no danger of switching over to veggie to soon (and thereby possibly damaging the engine).
But is it for you? Hopefully this site can refer you in the right direction
Volkswagen has been the only manufacturer selling diesels cars in Canada or the US since 1999.
Running your Diesel on Vegetable OilPros