Comparing Diesel #2 to B5 - 2013 Volkswagen Passat TDI Long-Term Road Test
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2013 Volkswagen Passat TDI Long-Term Road Test

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2013 Volkswagen Passat TDI: Comparing Diesel #2 to B5

May 9, 2014

2013 Volkswagen Passat TDI

Scott's recent experience at a biodiesel pump got us both thinking. Would biodiesel make a noticeable difference in the performance or MPG of our 2013 Volkswagen Passat TDI?

A test was in order, but it seemed to me that the 5-percent biodiesel fuel (B5) allowed by VW might produce small differences that would be difficult to quantify. If I was to make sense of this I needed to control as many variables as possible. And I needed a fairly long route that would burn enough fuel to nullify any pump-shutoff inconsistencies.

Fortunately, I had a business trip to Las Vegas coming up, one that I had planned to drive to anyway. My time was spoken for all day Friday and Saturday evening, but the bulk of Saturday was mine.

I decided to drive the TDI to Vegas Thursday afternoon on diesel #2 and park it in the hotel parking garage while I attended to my Friday obligations. Then, since I despise gambling and I'm behind on my audiobooks, I figured I'd use my free Saturday to drive BACK to my southern California starting point.

Once there I'd fill it with B5 biodiesel, turn straight around and retrace my route back to Vegas in time to make my evening appointment. After another overnight stay I'd head home and finish the B5 loop on Sunday morning.

It was a good plan, if not a bit insane, but then a fuel supply problem cropped up at the 11th hour.

2013 Volkswagen Passat TDI

I did everything to head it off, too. I searched online for a biodiesel station that sold both Diesel #2 and B5 biodiesel at a suitable location, which I defined as somewhere on the eastern edge of the L.A. basin. I found one in Ontario, California. and called ahead to make sure they sold diesel #2 along with the B5 (and B20) indicated by the Web site.

But that's not what I'm seeing now that I've arrived to top up with Diesel #2 and begin the first of two 458-mile round trips. There isn't a B5 pump here, just the same sort of B20 pump Oldham saw in San Jose. Now what?

And I've still got another problem. But this one I already knew about: How will I dispose of the unburnt diesel before I make the switch to B5? I'd already decided that draining the tank or siphoning fuel wasn't going to be practical. And the first round-trip to Las Vegas, long as it is, won't burn three-quarters of a tank, let alone drain it. There's going to be some Diesel #2 left in the tank unless I drive an artificially long route or drive extra fast, neither of which seems like a good idea.

Wait a minute. Problem solved. The lack of a B5 pump is in reality a two-birds-with-one-stone solution.

When I come back after this first loop I'll ignore the diesel remainder in the Passat's 18.5-gallon tank. It won't matter. I'll just pump in exactly one-quarter of a tank of B20 (4.625 gallons), then finish the fill at the same Diesel #2 pump I used at the start. I'll brew my own B5 cocktail right in the tank. Loop One consumption will simply be the sum of the amounts dispensed at the two pumps.

Each loop will have the same mileage, same route, same elevation profile, same time of day for the outbound and inbound legs, same temperature and traffic profile, same lunch stops and, now that I've encountered this B5 "problem," the same pump shut-off calibration for all top-off readings.

Excuse me while I hit the road. I've got some driving to do.

Dan Edmunds, Director of Vehicle Testing @ 19,711 miles

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