What is it?
Rudolf Diesel designed his engine to run on vegetable oil. You can still do it today, but some modifications to your diesel vehicle will be necessary (it’s not possible with petrol vehicles). Veg oil is too viscous to use directly in an unmodified vehicle, so there are two ways that viscosity can be reduced:
- by removing glycerine to make biodiesel (see biodiesel factsheet), in which case no conversion is necessary
- or by converting the vehicle to use straight oil (which reduces viscosity by pre-heating the fuel)
Biodiesel can be used in any diesel vehicle, and mixed with mineral diesel in any ratio. Straight vegetable oil should not be used in an unconverted diesel vehicle, due to its viscosity, and the fact that the glycerine content may cause ‘coking’ of fuel injector heads and possible engine failure. It’s perfectly legal despite the reports of arrests in Wales for driving on veg oil. They weren’t paying road fuel duty on the oil. BUT since June 07 there isn’t any duty payable for anyone using less than 2500 litres.
What are the benefits?
Vegetable oil is a biofuel, and as such is virtually carbon-neutral. This means that the carbon dioxide (CO2) released when the fuel is burnt is absorbed by the plants that will provide the next crop of oil. As CO2 is the main greenhouse gas, switching to biofuels can help to slow down global warming. Emissions are cleaner too – sulphur is eliminated, and a range of other pollutants are reduced dramatically (including particulates, carbon monoxide, and unburnt hydrocarbons). Further benefits include: requires less energy to produce; doesn’t have to be transported such large distances; renewable resource; non-toxic; and biodegradable. These environmental benefits also apply to biodiesel, but if you’re sure that your car is worth a conversion to be able to use straight vegetable oil, this is a more environmentally-friendly option, as there will be none of the problems associated with the waste from the biodiesel production process.
What can I do?
With a petrol car, nothing – veg oil is for diesel vehicles only. To find out which cars can be converted, see DieselVeg. You can buy cooking oil in supermarkets, although we don’t recommend virgin oil for environmental reasons. Goat Industries sell cleaned-up used oil in bulk (oil drums). The 2 main pump manufacturers in the UK are Bosch and Lucas. To run on veg oil a Bosch pump is preferable. Lucas pumps have a ‘paddle’ mechanism which can’t cope with the heavier veg oil. A good mechanic can swap a Bosch pump for a Lucas.
An extra tank is added for veg oil. You start with diesel, then switch to veg oil when the engine is hot, and it is continually heated via a heat exchange system. Before stopping, switch to the diesel tank again so that there will be mineral diesel in the fuel line when you come to start your car again. Cost installed c. £800. DIY kit c. £400.
Simple one-tank method:
It’s simpler – you don’t have to remember to switch to mineral diesel near the end of your journey, and veg oil and mineral diesel can be mixed in the same tank. A simple one-tank conversion involves pre-heating the oil before it gets to the cylinders, and is only possible with indirect injection vehicles (D, TD, not DI, TDI, HDI, SDI etc), because they have a separate chamber for atomising the fuel before it reaches the pistons, so cold starting on veg oil is fine; also, a new, wider fuel line is installed between the fuel tank and the heat exchanger, because of the extra viscosity of vegetable oil. Cost installed c. £600.
Elsbett one-tank method:
German kit with a few installers in the UK. They have designed an engine where veg oil is the fuel and the coolant, so it gets continually heated. When starting from cold, there is an electrically-heated jacket on the fuel filter. They say no used oil. In a conventional diesel engine, fuel is initially sprayed onto a heater plug at the top of the chamber (which is why you have to wait a few moments for the plug to heat up when starting a diesel engine); in an Elsbett conversion, the heater plug stays on until the engine is up to temperature. Cost installed c. £850-1300, depending on vehicle. DIY kit c. £550-750. More difficult than the other two conversions – a job for experienced mechanics only
In June 2007, the road duty for biofuels was removed for anyone using 2500 litres or less. Contact HM Revenue & Customs for advice.