Biodiesel: A Guide

Biodiesel is an exciting alternative fuel that can be used as a supplement to traditional diesel fuel that offers dramatically lower emissions and is renewable.  But, running it isn’t always simple.  This guide overviews some biodiesel basics and which cars should or should not use biodiesel.

To start, it should be explained what biodiesel is and isn’t. Biodiesel is diesel fuel made from a biological source that’s been put through a refining process to create a mono-alkyl ester—soybean oil, rapeseed oil, peanut oil, vegetable oil, even sewage sludge and algae can act as feedstock for biodiesel. About half of the bio consumed in the US in 2014 so far has come from soybean oil.

Biodiesel is not Waste Vegetable Oil, although you can make biodiesel from it (and increasingly WVO is serving as a feedstock for bio). WVO is, in general, a less refined, dirtier, and less regulated fuel source. To be sure, biodiesel and WVO are two very different products, one involving a refining process and a requirement to meet ASTM standards, and another requiring only that it be filtered through someone’s old jeans. The refining process for biodiesel involves reacting an alcohol (usually methanol) with the oil.

For a much, much more comprehensive introduction to Biodiesel, check out the Biodiesel Basicssection on They’ve done an excellent job explaining exactly what biodiesel is and where it comes from.

Biodiesel Benefits

  • Bio is better for the environment than normal diesel. It’s sustainable, produces 57% less emissions, and nothing is wasted in the refining process.
  • It isn’t made from fossil fuels.
  • If you’re buying bio in the USA, odds are it’s been grown and refined in the USA, so it supports the US economy and local businesses.
  • Lubrication. Biodiesel has lubricant properties and a far higher lubricity than ULSD (ultra low sulfur diesel).
  • Regulated and produced to ASTM standard D-6751, which ensures consistent quality.

Biodiesel Drawbacks

  • In the wrong blend, it could harm your car. This is obviously the main drawback. Possible problems include damage to injection components, damage to emissions systems, and fuel seeping into your oil. Different cars can handle different blends, and in the section below we’ll detail how compatible different diesels are. Bio has different physical characteristics compared to normal diesel: different viscosity, different solvent properties, different moisture content, different flashpoint. Because of these differences, however small, you may run into trouble.
  • It gels at a higher temperature than normal diesel, which makes it more difficult to use in the cold. B100 (100% biodiesel) will gel at 32 degrees F, 0 degrees C.
  • Biodiesel fuel quality can vary, just like petrodiesel, even though it’s supposed to meet regulatory standards.

Biodiesel in Common Rail TDIs

Newer VW TDIs, those with common rail engines (2009+) are only rated to use B5, or 5% biodiesel, 95% normal diesel. Anything more will void your warranty.

There are several reasons for this, the major reason being something called oil dilution. Many 2009+ common rail cars use post-injection as part of the emissions process: a small amount of fuel is squirted into the cylinder during the exhaust stroke in order to clean the DPF (diesel particulate filter). The fuel vaporizes in the cylinder, but doesn’t burn until it it’s in the emissions system. With biodiesel, people began noticing oil dilution in their fuel, and realized that either fuel or water were not leaving the cylinder and traveling to the emissions system, but instead were adhering to the cylinder walls and eventually ending up in the engine oil sump. Over time, the water/fuel was building up in the engine sump and diluting the oil. Diluted oil can’t do its job, and your engine could wear out much earlier or seize.

Undoubtedly, diesel drivers and manufacturers are going to seek to remedy this relatively new problem, although it’s probably not #1 on VW’s list. Diesel drivers seeking to use biodiesel in more substantial blends will have to turn to the earlier TDIs.

Biodiesel in earlier TDIs

Before the common rail injection system, VW made TDIs from 2004-2006 with a different injection system, referred to as Pumpe-Düse, or PD. PD cars had higher engine pressures and more sensitive injectors, so many worried about their compatibility with the different physical characteristics of biodiesel. However, many people reported using blends of 50% or more biodiesel in these cars without consequence. Others had problems they believed were related to biodiesel. In sum, use your judgment—a more cautious biodiesel user could probably run B20 and be able to avoid any problems.

The earlier TDIs, from 1997 through 2003, are much more compatible with biodiesel, because of their lack of emissions equipment and simpler injection systems. TDIs up until 2004, when VW switched to the BEW engine with a Pumpe Düse fuel pump, are compatible with B100, or 100% biodiesel. The only problem you may notice is a that you might need to change your fuel filter after the first couple thousand running B100—biodiesel dissolves some deposits left behind inside engine from normal use. It’s also recommended that you don’t switch back and forth between B100 and normal diesel, because the fuel’s differing effects on the injection pump components could cause it to leak. Other than that, go nuts! Being able to use biodiesel is one of the many perks to owning a TDI.

Newer Mercedes

2004 and newer Mercedes with BlueTec engines are only approved for up to B5 blend biodiesel, which is unfortunately a very small amount. Manufacturers are obviously going to be conservative with their rating for biodiesel, but newer Mercedes have post-injection and high-pressure injection systems just like the newer VWs, so they’re subject to the same limitations.

For our part, we’ve never heard of newer Mercedes drivers using blends with a significant amount of biodiesel in them. Most people strongly recommend against it. These cars are expensive, and people don’t want to risk messing them up by running bio if they’ve been told it could hurt their vehicle (which it very well could).

Older Mercedes

Way over on the other end of the spectrum, Mercedes diesels from 1999 and before are perhaps better suited for biodiesel application than any other car. The older the better, in this case. Their injection systems are simple, they’re durable, and there’s no complicated emissions post-injection going on to cause fuel/water to get in the crankcase. If you want to run bio these cars, like the earlier TDIs, are a great option.

Chevy Cruze Diesel

The new Cruze diesel is manufacturer approved for up to B20. These cars are still new, so there’s not a lot of reports about biodiesel’s effect on these engines, but Cruze drivers should feel confident using at least B20. We’re not entirely sure how they’ve managed to avoid the oil dilution problems that occur in VWs and Mercedes common rail cars, but we’re interested to hear what people have to say as time goes on and more people drive these cars on bio. The Biodiesel Board of America was so excited about the Cruze being able to run B20 that it gave Chevy an award.

Jeep CRD

Like Mercedes and VW, Jeep only recommends up to a blend of B5 in their CRDs. This time, though, the manufacturer is definitely erring on the side of safety: many people have reported no problems using blends on their CRDs for extended periods of time and swear by biodiesel.

Sprinter Van

Again, we run into the sad problem of oil dilution with the common rail Sprinter Vans. They’re approved only to B5.

That doesn’t mean people don’t run higher percentages of bio in their Sprinters. Many drivers take precautions, such as changing the fuel lines to avoid harm from bio’s solvent qualities, changing oil more often, and checking for contaminants.

Overall, results have been mixed. Some people report their van running well on biodiesel, and others have reported numerous problems. Again, this is a situation where you have to use your own judgment and do some research before you decide to put bio in your van.


So, as we’ve seen, biodiesel compatibility varies from car to car (to van). The bottom line is that biodiesel can be a great, sustainable fuel source, but only if its compatible with your engine. Hard data is difficult to find, and often times doesn’t exist, so if you’re wondering whether or not to use biodiesel in your car, do your homework and use your best judgment.  Hopefully these guidelines will help.


Excellent resource for information on biodiesel. Also, there’s a tool for finding your local biodiesel station.

Biodiesel Magazine

Industry magazine for biodiesel. Includes interesting articles on biodiesel’s effect in newer emissions systems and common rail diesels.

Article on Converting your Sprinter Van to Biodiesel

Well-written article with 5 tips on how to prepare your Sprinter Van for biodiesel use.

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