Using Biodiesel

It is often said that biodiesel can run in any diesel vehicle with absolutely no modifications required. I have also heard it said many times that some sort of "conversion" is required in order to run biodiesel. Obviously there is a lot of confusing and conflicting information out there about biodiesel, and widespread misperceptions. I've written this page to try to clear up some of the myths you may have heard, and to educate our biodiesel customers about their fuel and how to use it properly, to ensure a great experience.

People who suggest that a "conversion" is required are probably confusing biodiesel with straight or waste vegetable oil (SVO/WVO). Biodiesel can be put directly into any diesel vehicle, and it will run in the diesel engine just like petroleum diesel-- and some vehicles can make the switch with absolutely no special maintenance ever required. For many other users, however, making some small and inexpensive changes to the vehicle (such as swapping out old rubber fuel lines) will eventually be necessary, and doing them pre-emptively will avoid letting them develop into problems.

Being aware of biodiesel's basic properties as a fuel will help every user be prepared for and avoid potential expenses and hassles.Use this shortcut menu, or scroll down the page, to find information about the following topics. Items that do not have active links are coming soon!

Information for ALL vehicles

Model-specific information


Cold weather properties of biodiesel

All diesel fuels can cloud and gel if exposed to temperatures below their gel points. People from places that get very cold in the winter, such as Alaska or Canada, will recall that even petroleum diesel has to be winterized during very low temperatures, or it will gel up and your vehicle will not start. The same is true for any blend of biodiesel. The cloud point and gel point of a specific batch of fuel depends on many things, including the type of oil it is made from, and whether or not it has been winterized in some way. Common methods of winterizing include blending in additives such as kerosene, or pre-separating out the most waxy molecules in the fuel by a process known as cold-fractioning.

snow driving

If biodiesel is allowed to reach its cloud point, wax crystals will begin to form in the liquid fuel, giving it a whitish opaqueness, just like a jar of olive oil left out in the cold. If the temperature goes just a few degrees below the biodiesel's cloud point, then it will reach its gel point, at which time part or all of it will become a waxy solid.

Clouded or gelled biodiesel can be restored to liquid fuel, but in order to do so, it must be warmed up to a temperature that is significantly higher than its cloud point. Even if the fuel warms up enough to turn liquid again, there may still remain some bits of waxy solids that will sink to the bottom of the tank, unless the fuel gets heated to a much higher temperature that is sufficient to fully melt the gelled bits. Meanwhile, if these bits get sucked into the fuel filter, they can clog it. The best practice is to never allow your biodiesel gel inside of your vehicle.

How can you avoid biodiesel gelling? It's simple: pay attention to the cloud and gel points of the fuel you purchase. A reputable supplier of high-quality biodiesel will have this information readily available to you. Make sure you only buy biodiesel that works for the current climate in the area where you plan to drive. If you plan to drive somewhere (such as Lake Tahoe) where the temperature may be colder than your gel point, blend in some petroleum diesel, which is usually good down to around 10°F. If you have any questions, call us for advice!

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Solvent properties of biodiesel

Biodiesel, unlike petrol diesel, is a good cleaning agent. This is ultimately one of biodiesel's benefits, but if your car has been running on regular diesel for a long time, it may cause you some trouble initially. Most gas stations don't filter their fuel very much, so a lot of dirt and small particles are allowed into your gas tank. As long as you are using petrol diesel, this debris will just sink to the bottom of the tank and sit there. But biodiesel, being a good solvent, will dissolve all of the old accumulated dirt out of the bottom of the tank. Your vehicle's fuel filters will then catch and trap the debris, before it reaches your engine.

fuel filter

If your car has been on petroleum diesel for a long time, there is probably enough debris in your tank to clog your fuel filters at least one, if not more than once. When first making the switch to biodiesel, especially if your car is more than a couple of years old, you should expect your fuel filter to potentially clog.

There are several ways of preparing for this and avoiding trouble. One is to purchase an extra set of fuel filters, and learn how to change them yourself. The Biofuel Oasis in Berkeley gives periodic workshops on changing fuel filters; see their website for more information. Another possibility is to have your mechanic change your fuel filters, after you've run through your first few full tanks of biodiesel but before you experience clogging.

A clogging fuel filter will cause your car to lose power, usually in spurts or sputters, and especially in places where you try to open up the throttle more (such as going uphill), because the amount of fuel able to pass through it will be limited. If you feel your fuel filter beginning to clog, have it changed as soon as possible.

Biodiesel's solvent properties can also flush more than just debris from tanks. If a fuel tank is rusty inside, or if it has an algae or bacteria infestation, these things will also flush out, and in this case more extreme measures should be taken. If you experience unusual or persistent fuel filter clogging even long after you've switched to biodiesel, or if you find red (rust), green (algae), or mucous-like (bacteria) deposits in your filters, you may need to have a mechanic remove the fuel tank and clean it. The tank can be boiled out by a radiator shop, or cleaned with a strong acid solvent and some nuts and bolts used to knock the debris loose. Algae and rust are most common in cars in coastal areas that were not used very often, or spent a long period of time sitting idle. There are also biocides and other tank-cleaning additives that could provide a cost-effective solution. If you need advice, you are always welcome to call us first to talk about it.

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Lubricating properties of biodiesel, and ULSD warning

Biodiesel is a good lubricant, which is very good for engines, fuel-lubricated injector pumps, and any other moving parts that come into contact with the fuel. It will also tend to lubricate and expand any seals that it comes into contact with.

injector pump seals

Ultra-low sulfur petroleum diesel (ULSD), on the other hand, will tend to shrink and harden seals. All diesel sold in California is ULSD, due to emissions standards. ULSD does have additives to improve its lubricity, but it has still been reported to cause injector pump failures for vehicles with fuel-lubricated pumps.

Switching back and forth between 100% biodiesel and ULSD can exacerbate this problem. If seals are expanded and then shrunken too many times, they may eventually become damaged and begin to leak. Going back to 100% biodiesel might (or might not) allow a leaking injector pump to re-seal. Some people suggest running some B100 through, and then allowing it to absorb for at least 24 hours before giving up and commiting to an expensive injector pump repair or replacement.

The best way to avoid this problem is to avoid ever using 100% ULSD petroleum diesel in your car. If you are traveling to a place where you need to blend petroleum diesel with your diesel in order to avoid gelling, or because you aren't able to find biodiesel in the area, try to keep at least 25% biodiesel in your tank. Remember, biodiesel and regular diesel can be blended in any proportion, so it is no problem to fill up with regular diesel when your tank is still half full of biodiesel.

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Compatibility with rubber and other materials

fuel filter

Like any fuel, biodiesel is not compatible with all materials, and should only ever be stored in or used with approved containers. Certain plastics are ok and others are not. Most modern seals and hoses are fine with biodiesel, but natural rubber is not. Biodiesel will corrode natural rubber over time, and cause it to become soft and leaky.

Vehicles manufactured before the mid-90's, and a few newer diesel cars, may have fuel lines made of natural rubber. Use of biodiesel will cause these lines to become spongy and soft, and eventually to leak. Rubber fuel lines and other rubber seals should be replaced with newer, synthetic Viton material, or A1-grade Marine fuel lines, which are biodiesel safe.

Volkswagen TDIs and most other newer diesel cars and truck have biodiesel-ready fuel systems straight from the factory. But if you're not sure about your particular vehicle, ask a mechanic who is knowledgable about biodiesel. See our Bay Area Resources page for some recommendations.

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Special warning for 2007-2010 vehicles

Save Biodiesel

Unfortunately, most diesel vehicles available in the United States since late 2007 are equipped with a new type of emissions system that can cause serious problems when using biodiesel. Sadly, this includes the 2009 and 2010 Volkswagen TDIs, 2007.5 and newer Dodge trucks, and others. The cause of the incompatibility is related to the diesel particulate filter (DPF), and a post-combustion injection cycle that some manufacturers are using in its regeneration cycle. While it is possible to safely use these vehicles with high-blend biodiesel under certain driving conditions and with proper monitoring, we cannot recommend this for most drivers due to the level of extra attention that would be required.

***  Please visit to learn more about this issue and what you can do about it.  ***

To find out if your specific 2007 or newer vehicle is equipped with a DPF that uses a post-combustion injection cycle directly into the engine, we recommend contacting a competent mechanic such as one of those listed on our Bay Area Resources page, or contacting the manufacturer directly. To find out how you can monitor your DPF-equipped car to make sure you are using biodiesel safely, please refer to the FAQs page on the Save Biodiesel website, and call or send us an email.

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