Simanaitis Says

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WHEN B20 biodiesel is discussed, I am reminded of Dirty Harry, Clint Eastwood’s character, saying to the punk, “You’ve got to ask yourself a question, ‘Do I feel lucky?’”

This, in effect, is what Volkswagen/Audi warranty managers—and their diesel customers—are saying with regard to B20 biodiesel. By contrast, Mercedes-Benz, the first and oldest manufacturer of diesel passenger cars, says its warranties are voided on anything beyond the lesser-bio B5 variety.

As background, biodiesels are blends of conventional petro-based middle distillate and bio-sources vegetable oils, microalgal oils or animal fats. B5 has as much as 5 percent of the latter. B20 is 20 percent bio and 80-percent petro-diesel.

There are related controversies with ethanol-enhanced gasoline blends, E10, E15, E30 and E85 (see and its references). Similarly, the concerns with biodiesel center on the bio proportion. Generally, it’s not a problem in many states where diesel is at most B5 (and often B0, free of any bio enhancement).

In other states, this controversy isn’t new.


This Mercedes-Benz C220 BlueTEC, a rarity in Illinois, is not compatible with this Illinois fuel.]

Two years ago, Mercedes stopped allocating BlueTEC diesels to its Illinois dealerships (including the major Chicago market). The Midwestern farm lobby had encouraged tax and other incentives which in turn resulted in bio enhancements averaging around 11 percent.

Mercedes warns that biodiesel seepage into the crankcase can form acids that degrade into engine-fouling sludge. At this point, the company warranties its BlueTEC diesels for B5. Anything beyond B5 voids the warranty—with possible exceptions depending on the car’s service record.

“Do I feel lucky?”

Things aren’t going to get any better. Minnesota has a similar farm-lobby mandate taking effect in June 2014 that will require in excess of B10 at that state’s diesel pumps.

In the meantime, Volkswagen and its corporate sibling Audi are pushing to popularize diesels beyond their current 3 percent of the U.S. market.


Volkswagen Golf TDI, above left, and Audi A6 TDI now have warranty coverage on up to B20. So does the Chevrolet Cruze Diesel, below.


VW/Audi warranties originally required no more than B5. However, TDI turbodiesel owners have received letters saying that any damage caused by as much as B20 will now be covered. To keep the warranty in effect, more frequent oil filter changes have also been mandated.

In a sense, VW/Audi warranty managers are saying, “Do I feel lucky?” And, given the inconvenience of a failure, so are the owners.

Automakers are researching how to make diesel engines more amenable to heavier bio enhancements. However, the changes are non-trivial and costly; things like redesigned crankcases with more oil capacity.

The authoritative trade journal Automotive News discussed this matter in its September 2, 2013 issue. Quoted is William Woebkenberg, fuels policy director, Mercedes-Benz U.S.A., who says, “It becomes a study in risk management.” ds

© Dennis Simanaitis,, 2013

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