If you have a diesel car, it is possible to run it on used vegetable oil. Because vegetable oil is really thick, it has to be thinned out so it doesn't damage your car's fuel injection system. The simplest way to reduce the viscosity of the vegetable oil is by mixing it with a lighter fuel such as kerosene.
Filter out any bits and pieces of food from your used vegetable oil by pouring it through a strainer.
Mix three parts of used vegetable oil with one part kerosene.
Let the mixture stand for a week before using it. Don't mix the kerosene and vegetable oil; letting it sit for a week will allow it to mix properly.
Used vegetable oil has been found to work better in cars than new vegetable oil.