The only reason you can’t run your car on straight vegetable oil is the viscosity.
It’s OK when hot, but too thick when cold. So you have two choices – either you modify your car or modify your fuel.
If you are going to modify your car, you simply add an extra fuel tank for starting and stopping. You start the car on regular diesel, then when the motor is warm you switch over to the oil. Before you stop, you then just switch back to the diesel.
This is a little like having a dual fuel car, so all the switches and valves and solenoids are readily available. The only decision you need to make is where you’re going to put the extra fuel tank. Because it’s only used for starting and stopping, it doesn’t need to be very big – 10L is plenty. On older cars, a popular spot is inside the engine bay.
The only other modification you need to consider is heating your fuel lines, so the thicker oil can flow from your tank to the engine bay. This is generally done by branching off your cooling system, and it’s possible to get tube-in-tube designs where the fuel line is encased with a cooling line.
The acronym for this option is SVO (Straight Vegetable Oil) and there are plenty of online forums around where the logistics of this process are discussed.
The idea, of course, is that you use waste cooking oil as your fuel, which can be obtained from fish and chip shops and restaurants.
It’s not as easy to get as it used to be, however, as there are now lots of people making their own fuel, so you might have to do a bit of scoping around to find a supplier.
One option of course is fat. Fat is much easier to obtain than cooking oil, as it is more commonly used (and is cheaper).
There are two obvious problems with fat, however – how do you collect it, and how are you going to get it into your tank as fuel?
One option would be to fit an tank into the boot of your car with a wide mouth or clip on lid. Into the bottom of your tank you run a line from your cooling system, so it would melt the oil. With this approach, having a heated line would be mandatory, to stop the fat solidifying as soon as it left the tank.
Tomorrow we’ll look at the other option – modifying the fuel.