Biodiesel Compatibility

By Rick Da Tech


Can I Use Biodiesel in My Car?Almost every diesel vehicle on the road came from the factory biodiesel compatible. So all you really need to do is put the fuel in the tank. There are some really old diesels that were produced before low sulfur diesel was introduced that have fuel lines that are not compatible with biodiesel. They will be easy to spot. The fuel lines will be leaking and wet and greasy from fuel on the outside of the fuel line. Since 99.9% of all diesels are biodiesel compatible, the best course of action is to just keep an eye on things and watch for leaks then fix leaks in a timely manner.
There are some issues specific ways that biodiesel is different from diesel. Those differences can cause problems, if we don’t pay attention to the differences.  

  • Biodiesel has a higher gel point
  • Biodiesel can plug filters
  • Diesel Particulate Filters 




Gel Point

The concentration of saturated fats in biodiesel determines its gel point. The more saturated fats, the higher the gel point. Biodiesel usually has enough saturated fats to cause the fuel to gel up faster than diesel fuel. There are two ways this can be a problem for biodiesel. First, small particles of frozen biodiesel pass through the fuel lines only to plug up the fuel filter. This causes air locks in the fuel system, stalling out the engine. The whole vehicle has to be warmed up before it will run again. The second method is more of a problem for vehicles with heated fuel filters. As the temperature drops fuel in the fuel tank will freeze and form a ball that rolls around in the bottom of the tank. Being on the bottom of the tank, it can plug up the fuel lines at the tank. This causes a strong vacuum to be pulled on the fuel lines, which were not designed to handle a vacuum. They leak causing an air lock and the engine stops. To read more on how to prevent these problems check out the article on Winter Biodiesel.

Filter Plugging

I like the way Dr. Dan put it. Biodiesel is a laxative. Any crap that gets in the tank will end up in the filter. The fuel filter can plug and your car may or may not quit running and it could damage other components in your engine if not addressed right away. The thing we have to watch out for is buying unfiltered diesel. Fuel purchased from gas stations are not really filtered adequately. If they have a filter at all, it will be 30-40 micron, just enough to protect the pump. Sometimes the station will bypass the filter to keep from having to replace it. Trash from the station's tank can make its way into the fuel tank. To protect your fuel system, make sure you use a 5 micron filter.

As preventive maintenance, change out your fuel filter every time you change the oil. In addition change out the fuel filter any time you have any problems with the engine or notice it running differently, since that will most often solve the problem. Many diesel mechanics will actually replace the IP before they change out the filter, so it’s important to monitor the fuel filter. Some vehicles have a sensor that detects fuel filter plugging. Most don’t. If you start having filter pluggin problems after buying petrol diesel, have your tank cleaned out or will keep replacing filters without end.

The fact is, almost all IP damage is ultimately caused by running clogged filters. The pumps are lubricated by fuel passing through them and if the filter is plugged, the IP is not lubricated and can fail.

There are a couple of vehicles that are more susceptible to filter clogging than others. The Dodge Sprinter and the Duramax Diesel both have grossly undersized filters that are quick to plug.

Diesel Particulate Filters

The newest diesel vehicles have a pollution control device on them called a Diesel Particulate Filter (DPF). It is a device located in the exhaust system that traps soot. Eventually it will build up enough soot to restrict the exhaust. When that happens, the computer will spray some fuel into the DPF to burn out the soot. If the fuel is sprayed directly into the exhaust just before the DPF we don’t have any problems. All of the fuel ends up being used to burn out the soot. Some manufactures decided to save a few bucks and use the existing fuel injectors to spray fuel into the cylinder on the exhaust stroke (aka in cylinder post injection); resutling in some of the fuel not making it out of the cylinder or through the exhaust manifold, or through the turbo. This means they have to dump much more fuel into the cylinder than they would if they spent a few extra bucks for one more spray nozzle.

The first problem is that some fuel doesn’t go out the exhaust port. Some will actually leak past the rings and dilute the engine oil with biodiesel. This can be a serious problem, causing engine damage if not addressed. If your vehicle has a DPF and operate on biodiesel, then you may need to increase the frequency that you change your oil

One thing to note is that when diesels are driven for short trips, they create more soot than diesels driven for longer trips. That’s because the engines run cold most of the time on short trips. So, the computer will want to dump fuel into the DPF more frequently on vehicles used for short trips. The more frequently it dumps the more of a problem oil dilution becomes. As an example the DPF may need cleaning once every twenty miles on diesels used for one mile trips, while a diesel used only for 20 mile commutes may only need to clean out the DPF once every 10,000 miles. That’s a big difference and means the difference between a clean burning long lasting healthy diesel and an expensive dirty diesel that’s always in the shop.

Related Links

Dr Dan's Biodiesel Videos - a dozen videos that discuss biodiesel compatibility with common diesels.

Biodiesel, Passenger Cars & Trucks - The National Biodiesel Board discusses biodiesel in passenger vehicles and the latest OEM warranty positions.

Using Biodiesel Fuel in your Engine - Penn State document answering how to make the most out of biodiesel

Impacts of Biodiesel Fuel Blends Oil Dilution on Light-Duty Diesel Engine Operation  NREL 2009


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