Diesel engines were originally designed to burn vegetable oils, and today's engines can safely use diesel with cooking oil added. Mixing cooking oil with diesel can reduce costs and will burn cleaner than straight petroleum diesel. Restaurants typically have to pay to dispose of their used cooking oil, so you can usually collect used cooking oil for free by merely asking. After collecting used cooking oil, you will have to filter it to prevent damage to your engine.
Ask local restaurants for their waste oil and set a schedule to pick it up from them regularly. Talk to the manager and explain what you are doing. Generally, any manager will be happy to give you waste cooking oil for free. Look for restaurants that go through a lot of oil; fast food and Chinese restaurants are great for this. Ask them to pour the cooking oil back into the container that it came in.
Let the cooking oil sit for at least a week in its container, so that impurities can settle out. This will make it much easier to filter; the longer it sits, the better.
Slowly pour the oil from its containers into the first 121 litre (32 gallon) bin. Be sure to work carefully and avoid pouring the settled dregs into the garbage can.
Using the immersion heater, increase the temperature of the oil to a minimum of 71 degrees Celcius (160 degrees Fahrenheit). This will thin the oil and make it pass through the denim more easily while leaving impurities behind.
Cut the legs off a pair of denim jeans and close off the bottom of each leg very tightly with a zip tie. Cut a hole in the top of the legs, from which you can hang them with the bungee cords. Put one leg inside the other to form a double filter, and hang this above the second 121 litre (32 gallon) bin.
Attach the garden hose to the utility pump and submerge the pump into the oil. Place the other end of the hose in the top of the denim filter. Turn on the pump and let the oil filter through the jeans into the second bin. Let the filtered oil sit overnight so that any water present in the oil will sink to the bottom.
Add the filtered cooking oil to your diesel fuel. Avoid using oil from the bottom of the bin, where water has collected.
In cold weather, use less cooking oil to ensure that your engine will start, or warm the fuel before starting the engine with an engine block heater. Different engines will tolerate different percentages of cooking oil. Start with about 20 per cent cooking oil and gradually increase to determine what your engine can handle. If the engine begins to start or accelerate poorly, reduce the percentage of cooking oil by adding more diesel. Keep a supply of sawdust or cat litter nearby to soak up any spill of cooking oil or diesel.
Make sure that your cooking oil is properly heated and filtered so that water and sediments are completely removed. Any water or impurities in the cooking oil will cause damage to your engine. Use rubber gloves to protect yourself from the toxicity of diesel and any bacteria in used cooking oil.