Biodiesel Compatibility



Can I Use Biodiesel in My Car?Almost every diesel vehicle on the road is biodiesel compatible from the factory. So, all you need to do is put the fuel in the tank. Some old diesel vehicles produced before low sulfur diesel was introduced may 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 keep an eye on things and watch for leaks.

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

Gel Point is the temperature at which a fuel starts to freeze into a solid. Gel point is determined by the concentration of saturated fats in biodiesel. 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. When biodiesel starts to freeze, it can cause one of two problems. First, small particles of frozen biodiesel pass through the fuel lines only to plug up the fuel filter, causing air locks in the fuel system and stalling out the engine. Second, as the fuel in the tank starts to freeze it will form a small ball of solid biodiesel that can plug the fuel intake line. The fix for both problems is to warm up the vehicle above the gel point temperature in a heated garage. For information on how to prevent cold weather problems read our 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, restricting flow. Your car may or may not quit running, and it could damage other components in your engine if not addressed right away. Buying unfiltered diesel is a leading cause of plugged fuel filters. Fuel purchased from gas stations is often not 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. A good first repair step for a poorly running vehicle is to change out the fuel filter. Many diesel mechanics will replace the expensive Injection Pump (IP) before they change out the fuel filter, so it's essential to monitor the fuel filter. Some vehicles have a sensor that detects fuel filter plugging. Most don’t. If you start having filter plugging problems after buying petrol diesel, have your tank cleaned out, or you will keep replacing the filter until you do.

The fact is, running a diesel engine with a clogged fuel filter is the leading cause of IP damage. Injector pumps are lubricated by the fuel passing through them. Running with no fuel means, no lubrication, and pump failure.

The fact is, running a diesel engine with a clogged fuel filter is the leading cause of IP damage. Injector pumps are lubricated by the fuel passing through them. Running with no fuel means, no lubrication, and pump failure.

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, it will spray fuel into the DPF to burn out the soot. If the fuel is sprayed directly into the exhaust just before the DPF, all the fuel ends up being used to burn out the soot.

Most manufacturers 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). With this design, all the fuel doesn't make it out the exhaust port, and biodiesel will leak past the rings and dilute the engine oil. Biodiesel in the engine oil is a serious problem, causing engine damage if not addressed. If your vehicle has a DPF and operates on biodiesel, then you may need to increase the frequency that you change your oil.

When diesels are cold they create more soot than when they are at operating temperature. If you drive your diesel mostly on short trips, it never warms up. This causes soot to build up quickly, triggering frequent dumps of fuel into the DPF, resulting in oil dilution. A 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 could mean the difference between a clean burning long-lasting healthy diesel and a 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