Veggie Oil Conversion

In March of 2007, Murray conducted a veggie oil conversion at the Hostel on Nikki and Jeremy’s car. A second fuel tank for the waste veggie oil was installed in the spare wheel well of their 2003 VW Jetta. The tank, along with the other conversion hardwear was made by Greasecar

One of the biggest differences between used veggie oil and diesel fuel is viscosity of the waste oil. Diesel is thin, flows easily and is easy to pump and inject into a diesel engine. Veggie oil, on the other hand, has the viscosity of honey and would pretty quickly gum up the injectors, the pump and any filters or fuel lines particularly on cool or cold days.

So the answer is to heat up the oil until it is the same viscosity as normal diesel and this is achieved in two stages. Firstly, back in the fuel tank in the spare tire well and again just prior to injection. The best and most reliable source of heat is the car’s coolant system. Water and coolant is pumped around the engine block to take the heat out of the engine, cooled in the car’s radiator and pumped back to the block. Most vehicles coolant temperatures are around 160 – 190 degrees so this is ideal. So we simply tap into the car’s interior heater feed pipe with a T-piece and feed a water hose back to the veggie tank.

Inside the tank is a simple two-turn copper coil so that this hot water can warm up the oil in preparation to passing it up to the engine. The return water pipe goes back to the engine and inserted in this is a piece of plex piping which caries the veggie oil, kept hot by the flowing water. It was made a little bit more complicated by routing the water pipes back to the engine compartment by concealing them up under the exhaust heat shield for the full length of the floor. instead of just fixing it to the underside of the car, where it would be vulnerable to being damaged.

So with the hot water lines and veggie oil line installed the next pice to install was the pre-heater that gets the veggie oil up to the final temp again, just before going into the fuel pump and subsequently, the injectors. Again, this is a water heated coil that surrounds the veggie oil filter. The hot water flows around the filter in a copper coil and heats the veggie oil to its final temperature prior to the fuel pump and the injectors.

Then two electronic valves are installed and wired to a three-way switch that allows you to select diesel, veggie or purge. The purge function is imperative as you never want the engine to cool down with veggie in the fuel lines. Purging simply forces diesel back up through the system to remove any veggie oil. Simply, you start on diesel, run until the engine and coolant is warmed up and then switch to veggie. When you stop, you simply purge for about 15 seconds, then switch to diesel and switch off.

All this is conveniently controlled from the dashboard adjacent to the veggies tank gauge we installed under the center dash, just under the air conditioner controls. We tested everything, did some preliminary test on diesel then once everything was warmed up, we switched to veggie. On road tests no significant change in performance was detected and if anything, the engine seemed to run a little quieter. Subsequent tests have proven that we are getting about the same level of fuel economy on veggie as we are on diesel, about 50 mpg. The car is capable of carrying 13 gallons of veggie oil as well as its normal diesel capacity giving a total range of about 1100 miles.

They seem to be getting good responses from the restaurants they have approached once they actually believe what they are doing! The used oil has to be filtered thoroughly, but that’s not much of an inconvenience for free fuel.