The Dirty Business Of Clean Diesels

by Paul Niedermeyer

Published: October 2nd, 2009

We get accused a lot of being anti-diesel. In reality, most of us love driving them. Paying for them is another issue. VW has just announced pricing on the new 2010 Golf VI, and the diesel premium is…premium. As in $4500. Strictly speaking, that investment also buys you a slightly lowered suspension (cost to VW: $0), and a slightly better audio unit (cost to VW: $50?). Here are the numbers: 2 door gas (2.5, 170 hp, EPA: 22/30) starts at $17,490; 2 door TDI (2.0, 140 hp, EPA: 30/41) starts at $21,990. Annual fuel cost savings are $362 for the TDI. Maintenance and repair costs favor the gas engine. Zero to sixty is similar with either model, with the gas (7.8 seconds) edging out the diesel (8.6 seconds) by a nose. The question we have is why not bring over VW’s excellent new 1.6 liter TDI engine, which makes 105 hp, and can easily top 50 mpg. Do diesel drivers prefer lowered suspensions and high(er) performance, or maximum mileage and a lower price?

Paul Niedermeyer

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Pch101 on Oct 06, 2009
MPG works for the consumer because it is a multipler against price. MPG is fine when comparing gas to gas, or diesel to diesel. It doesn't make sense when comparing diesel to gas. Adjustments are required, and most oil burning diehards don't bother making or understand the need for those adjustments. Not sure on the arm wrestle stuff; he/she might be built like Hulk Hogan (I’m not). Trust me, no need to fear broken limbs from me. But you won't have room for the beer in your bag; you can't face a Chicago winter without bringing a serious winter coat.

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Johnthacker on Oct 06, 2009
"Diesel would look about 15% worse if we used gCO2/km, since diesel has more carbon in a gallon than gasoline does, being more dense." The opposite is true. Please consult ComCar as an example. You misunderstood me; I apologize for being unclear. I'm not denying that diesel still has an advantage. I'm saying that diesel looks about 15% worse using gCO2/km than it does using MPG or any volume based unit. It still has an overall advantage, yes, but the advantage (as far as greenhouse gas emissions go), is not quite as large as the MPG numbers would imply. This makes it inaccurate for diesel backers to tout an advantage-- for greenhouse gas purposes-- using MPG alone. MPG works for the consumer because it is a multipler against price. & MPG is fine when comparing gas to gas, or diesel to diesel. It doesn’t make sense when comparing diesel to gas. You're both sort of wrong. For the latter, it depends in which sense you mean to compare them. MPG makes a reasonable amount of sense if you're a consumer who wants to know how far you can go on a gallon, and wants to compare pump costs. Consumers don't, in general, really care about greenhouse gas emissions. For the former, MPG is not a "multiplier against price." The information that consumers have is $/gallon. You want to use a unit that has gallons in the denominator in order to multiply by the price per gallon. The problem is that you have to divide MPG and $/gallon to get either $/mile or miles/$. Multiplying is, as you note, easier for consumers to do in their head. So for most consumers, gallons/100mi would be better for most purposes. You can multiply gallons/100mi by the posted $/gallon to get $/100miles, which is useful for most people. People consume miles (they really consume getting from point A to point B), they care about how many gallons it takes and how much it costs to go a certain distance. They generally don't care about how far they can get on a certain amount, or about greenhouse emissions directly. One exception is when people are considering the question "How far can I get on a full tank?"

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Pch101 on Oct 06, 2009
MPG makes a reasonable amount of sense if you’re a consumer who wants to know how far you can go on a gallon Fine. But it doesn't make sense to use it as an efficiency measure, which is the point that I've been making. Diesel fuel takes up less space, resulting in higher MPG. That isn't better or worse, just different. Comparing MPG between gas and diesel while claiming that one is more efficient than the other because of that MPG difference is illogical. Gas and diesel motors are both highly inefficient, in that most of the energy in the fuel is lost as heat and doesn't get converted into power output.

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PeteMoran on Oct 06, 2009

@ Pch101 ... you can’t face a Chicago winter without bringing a serious winter coat. My very first travel experience was to Chicago, and NOT having done my research, I did not bring anything close to "warm". I was then clearly identified as an under prepared tourist/traveller at the nearest retail shop. I was completely GOUGED for thermals, a suitable-for-the-Arctic warm coat & boots! The sales staff sniggered openly as I handed over the cash. Lucky I only carry a small amount of anti-USA bias from that event.... (Joking). @ johnthacker MPG is not a “multiplier against price.” ..... Multiplying is, as you note, easier for consumers to do in their head. Yes, "multiplier" was the wrong word. I intended to mean that the consumer could work it out easily. I should have just said that.

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