2013 Volkswagen Passat TDI Long-Term Road Test

Edmunds.com

2013 Volkswagen Passat TDI Long-Term Road Test

We ran two 458-mile loops to Las Vegas and back to compare Diesel #2 to Biodiesel. Here's what we learned.

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bodyshopboy

Bio diesel is an exciting prospect. I've read that algae-based bio eats waste and works as a CO2 sink actually using more CO2 that it produces. In the past Willie Nelson, the country music legend, had a vehicle that runs on hemp-based bio.

If true, it sounds like a miracle fuel.

agentorange

Wind will easily give a 10% variation in gas mileage. Drove a rental Corolla North from Las Vegas a few weeks back which is uphill and was into a very strong headwind. Thing barely made 30 mpg. The return trip had no wind and was downhill, but 42 mpg? It cannot be just the terrain.

misterfusion

Dan, this experiment was fairly insane (as you yourself pointed out), but I for one quite appreciate that you did it.

miata52

I think the wind explains most, if not all, of the difference.

bankerdanny

You guys seem to always have at least one diesel in your fleet, how about you try making your own biodiesel? I think C&D did it over a decade ago and it wasn't that complicated.

actualsize

I agree the wind may explain some or all of it. That's the trouble with any single-tank test, especially in our local deserts where the wind can vary wildly. That said, I have been talking to folks about Propel's version of B20 (though I have not yet interviewed anyone there myself...yet.) I'm told their B20 has a higher cetane level than straight diesel #2. Jay Kavanagh was skeptical of any improvement until he heard about the (alleged) extra cetane. I'm also told that cetane levels vary wildly in pump grade diesel #2 -- it's not regulated the way octane levels are regulated (and labeled) in gasoline. More digging is required, but it seems the results of any such diesel comparison may be harder to pin down.

allthingshonda

I like this test and the results are surprising. But you do know that VW can use this as an excuse for not approving warranty work on fuel related issues.

actualsize

One other thing about the wind: It only persisted for 100 of the 458 miles. I can't see it accounting for the entire difference when it only came into play for 22 percent of the miles driven.

fordson1

I think the other culprit is probably the fuel pump - I doubt the auto shutoff sensitivity on the pump you used is repeatable to the degree you would need in order to remove that as a variable.

azsoonerfan

Wind makes a huge difference. Try riding a bike in a strong headwind and then riding the same route when there is no wind, big difference in the effort required

actualsize

@fordson: we do many sorts of fuel economy tests using the same-nozzle technique before and after each loop. The difference here is a full gallon, but our experience tells us the shut-off of a given nozzle is repeatable to within a tenth of a gallon (or l

gilbed

What a great study. Thanks for doing this. I have been on the fence between a 2015 Mazda 3 hatch and the 2015 VW Golf TDI turbo diesel. I see mixed data on the eco-friendly nature of petrol diesel versus modern gasoline engines with respect to emissions, efficiency and fuel cost. I would love to get your feedback between these two cars. I like the concept of biodiesel and based on this study it sounds like this would be an option for the 2015 Golf TDI. Do you have any predictions on the future of biodiesel? Will it become more readily available? Thanks in advance for any and all information/insight you might have.