How to mix diesel and cooking oil

Written by joseph thiebes
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How to mix diesel and cooking oil
Add cooking oil to your diesel to cut costs and reduce emissions. (gas pump image by jedphoto from

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.

Skill level:

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Things you need

  • Cooking oil
  • 2 plastic bins, 121 litre (32 gallon)
  • 1 pair old denim jeans
  • 2 zip ties
  • 2 bungee cords
  • 1 immersion heater, 1000 watt
  • 1 submersible utility pump
  • 1 standard garden hose

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  1. 1

    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.

    How to mix diesel and cooking oil
    Fast food restaurants produce a lot of waste cooking oil that can be added to your diesel fuel. (french fries image by bright from
  2. 2

    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.

    How to mix diesel and cooking oil
    Let the oil settle for a week. (three sorts of oil image by Tomo Jesenicnik from
  3. 3

    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.

    How to mix diesel and cooking oil
    A standard plastic bin will do the trick. (recycling bins image by Alison Bowden from
  4. 4

    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.

    How to mix diesel and cooking oil
    Heat the cooking oil to at least 71 degrees Celcius (160 degrees Fahrenheit). (candy thermometer image by askthegeek from
  5. 5

    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.

    How to mix diesel and cooking oil
    An old pair of jeans will do the trick. Pick them up at a charity shop or use an old pair that you were planning to throw away. (blue jeans image by The Blowfish Inc from
  6. 6

    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.

    How to mix diesel and cooking oil
    Let the water and oil separate after filtering. (Abstract image of oil drops in water image by George Dolgikh from
  7. 7

    Add the filtered cooking oil to your diesel fuel. Avoid using oil from the bottom of the bin, where water has collected.

    How to mix diesel and cooking oil
    Adding cooking oil to your diesel can reduce emissions and decrease your costs. (leaf image by Jason from

Tips and warnings

  • 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.

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