Biodiesel is a diesel fuel that is made by reacting vegetable oil (cooking oil) with other common chemicals. Biodiesel may be used in any diesel automotive engine in its pure form or blended with petroleum-based diesel. No modifications are required, and the result is a less-expensive, renewable, clean-burning fuel.

Here's how to make biodiesel from fresh oil. You can also make biodiesel from waste cooking oil, but that is a little more involved, so let's start with the basics.

Materials for Making Biodiesel

1 liter of new vegetable oil (e.g., canola oil, corn oil, soybean oil)

3.5 grams (0.12 ounces) sodium hydroxide (also known as lye). Sodium hydroxide is used for some drain cleaners. The label should state that the product contains sodium hydroxide (not calcium hypochlorite, which is found in many other drain cleaners).

200 milliliters (6.8 fluid ounces) of methanol (methyl alcohol). Heet fuel treatment is methanol. Be sure the label says the product contains methanol (Iso-Heet, for example, contains isopropyl alcohol and won't work).

Blender with a low-speed option. The pitcher for the blender is to be used only for making biodiesel. You want to use one made from glass, not plastic because the methanol you will use can react with plastic.

Digital scale to accurately measure 3.5 grams, which equals 0.12 ounces

Glass container marked for 200 milliliters (6.8 fluid ounces). If you don't have a beaker, measure the volume using a measuring cup, pour it into a glass jar, then mark the fill-line on the outside of the jar.

Glass or plastic container that is marked for 1 liter (1.1 quarts)

Widemouthed glass or plastic container that will hold at least 1.5 liters (2-quart pitcher works well)

Safety glasses, gloves, and an (optional) apron

You do not want to get sodium hydroxide or methanol on your skin, nor do you want to breathe the vapors from either chemical. Both are toxic. Please read the warning labels on the containers for these products. Methanol is readily absorbed through your skin, so do not get it on your hands. Sodium hydroxide is caustic and will give you a chemical burn. Prepare your biodiesel in a well-ventilated area. If you spill either chemical on your skin, rinse it off immediately with water.

How to Make Biodiesel

You want to prepare the biodiesel in a room that is at least 70 degrees F because the chemical reaction will not proceed to completion if the temperature is too low. If you haven't already, label all your containers as "Toxic—Only Use for Making Biodiesel." You don't want anyone drinking your supplies, and you don't want to use the glassware for food again. Pour 200 milliliters methanol (Heet) into the glass blender pitcher. Turn the blender on its lowest setting and slowly add 3.5 grams sodium hydroxide (lye). This reaction produces sodium methoxide, which must be used right away or else it loses its effectiveness. (Like sodium hydroxide, it can be stored away from air/moisture, but that might not be practical for a home setup.) Mix the methanol and sodium hydroxide until the sodium hydroxide has completely dissolved (about 2 minutes), then add 1 liter of vegetable oil to this mixture. Continue blending this mixture (on low speed) for 20 to 30 minutes. Pour the mixture into a widemouthed jar. You will see the liquid start to separate out into layers. The bottom layer will be glycerin. The top layer is biodiesel. Allow at least a couple of hours for the mixture to fully separate. You want to keep the top layer as your biodiesel fuel. If you like, you can keep the glycerin for other projects. You can either carefully pour off the biodiesel or use a pump or baster to pull the biodiesel off of the glycerin.

Using Biodiesel

Normally, you can use pure biodiesel or a mixture of biodiesel and petroleum diesel as a fuel in any unmodified diesel engine. There are two situations in which you definitely should mix biodiesel with petroleum-based diesel:

If you are going to be running the engine at a temperature lower than 55 degrees Fahrenheit (13 degrees C), you should mix biodiesel with petroleum diesel. A 50:50 mixture will work in cold weather. Pure biodiesel will thicken and cloud at 55 degrees Fahrenheit, which could clog your fuel line and stop your engine. Pure petroleum diesel, in contrast, has a cloud point of -10 degrees Fahrenheit (-24 degrees C). The colder your conditions, the higher the percentage of petroleum diesel you will want to use. Above 55 degrees Fahrenheit, you can use pure biodiesel without any problem. Both types of diesel return to normal as soon as the temperature warms above their cloud point.

You will want to use a mixture of 20% biodiesel with 80% petroleum diesel (called B20) if your engine has natural rubber seals or hoses. Pure biodiesel can degrade natural rubber, though B20 tends not to cause problems. If you have an older engine (which is where natural rubber parts are found), you could replace the rubber with polymer parts and run pure biodiesel.

Biodiesel Stability and Shelf Life

You probably don't stop to think about it, but all fuels have a shelf life that depends on their chemical composition and storage conditions. The chemical stability of biodiesel depends on the oil from which it was derived.

Biodiesel from oils that naturally contain the antioxidant tocopherol or vitamin E (e.g., rapeseed oil) remain usable longer than biodiesel from other types of vegetable oils. According to Jobwerx.com, stability is noticeably diminished after 10 days, and the fuel may be unusable after two months. Temperature also affects fuel stability in that excessive temperatures may denature the fuel.