Biodiesel Compatibility

By Rick Da Tech


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. There are, however, some specific areas where biodiesel is different from diesel. Those differences can cause problems if we do not pay attention to them.

Fuel LInes

When the US mandated low sulfur diesel in 1993, the engine companies were forced to use higher quality materials for fuel lines.  Biodiesel is compatible with the factory low-sulfur and ultra-low-sulfur diesel fuel lines. It is highly unlikely that any of the vehicles made before 1993 still have their original fuel lines. However, some people put cheap vacuum hoses on their diesel engines as replacements.  These do not last with either biodiesel or the current ultra-low-sulfur-diesel and are easy to spot.  Look for leaking, wet and greasy hoses and replace them with high-quality OEM replacement fuel lines. Whether you run diesel fuel or biodiesel, it is a really good idea to pay attention to the general condition of your engine, including, looking for leaks.

Engine Warranties

Engine Manufactures warranty “materials and workmanship” of their engines. They do not warranty fuel systems or fuel.  However, if you use a fuel that they have not approved, then you run the risk of voiding the warranty for “materials and workmanship.” Personally, I do not see the relationship between fuel and wheel bearings, but apparently, they do. Most manufacturers approve blends of up to 20% biodiesel (B20) when blended using ASTM certified biodiesel. The National Biodiesel Board’s website keeps a list of which manufactures warranties allow biodiesel.


Gel Point

Gel Point is the temperature at which a fuel starts to freeze into a solid.  The concentration of saturated fats determines the Gel Point 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. When biodiesel starts to freeze, it can cause one of two problems. First, crystals of frozen biodiesel small enough to pass through the fuel lines but not small enough to make it through the filter, end up plugging the fuel filter.  Second, as the fuel in the tank starts to freeze, it forms 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 cloud 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 in his video, “Biodiesel is like a laxative, it’ll clean out your fuel tank; whatever is in your tank is going to end up in your fuel filter.”  So, it is a good idea to change your fuel filter after your first few tanks of fuel. If your fuel filter plugs, your car may or may not quit running, and it could damage other components if not addressed right away. Not everyone has filter plugging issues when they first start using biodiesel, but if you do, and it continues, then have your tank cleaned out.

Once you make it past your first few tanks of biodiesel, the leading cause of plugged fuel filters is buying dirty petrol-diesel from a gas station. Fuel purchased from gas stations is often not filtered adequately. Diesel pump fuel filters are 30-40 micron; if they have a filter at all. That is just enough to protect the pump. Sometimes the station bypasses the filter to keep from having to replace it. Trash from the station's tank can make its way into your fuel tank. To protect your fuel system, make sure you use a 5-micron filter.

The fact is, running a diesel engine with a clogged fuel filter is the leading cause of Injector Pump damage. The fuel flowing through an Injector pump lubricates it.  Running with no fuel means, no lubrication, resulting in injector pump failure.
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

Since 2007, diesel vehicles have come with a pollution control device on them called a Diesel Particulate Filter (DPF). It is a device added to the exhaust system to trap soot. Eventually, it builds up enough to restrict the exhaust. When that happens, it sprays fuel into the DPF to burn it out. 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.  Not all fuel systems are like this. “In-cylinder post injection” systems may not burn all the fuel in the DPF.  This system sprays fuel into the cylinder on the exhaust stroke using the existing fuel injectors. Since biodiesel vaporizes at a higher temperature than diesel, less of the fuel makes it out the exhaust compared to diesel fuel. The liquid fuel left behind in the cylinder leaks past the rings to dilute the engine oil. While this also happens with diesel fuel, it is more of a problem with Biodiesel. Fuel dilution of engine oil is a serious problem, causing engine damage if not addressed. If your vehicle has a DPF and operates on biodiesel, then depending on your driving habits, you may need to increase the frequency that you change your oil.

When diesel engines 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 completely. So, short trips cause 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 a diesel 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 diesel vehicles.

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