There are two ways of running on cooking oil. Firstly you can run on the oil as you get it. Secondly you can process it into something called Biodiesel.

Running on straight vegetable oil (SVO) or waste vegetable oil (WVO) has it's problems. The oil is much thicker than normal diesel fuel, particularly at lower temperatures. This can cause clogging of fuel lines and failure of fuel pumps. Most people running on SVO have heated fuel lines and also a tank heater. They also tend to run a two tank system so the vehicle can be started and stopped on normal diesel, so no SVO is left to clog in the fuel system.

The main problem with SVO is price. The oil is subject to tax in the UK much the same as ordinary petro-diesel, so there really isn't much financial gain from using it. WVO obtained from your local chip shop when they clean out the fryers is much cheaper (often free) but is not really suitable as a fuel. WVO would need a lot of filtering, but more importantly contains water and other chemical nansties which it picks up as part of the frying process. WVO really needs converting into biodiesel, which can be done by mixing with caustic soda and methanol. Although this sounds a bit complicated, it's actually quite easy. PM me if you would like to know more or search for 'making biodiesel' on the web.

Andy.