Originally Posted by amstrad
The objective of fuel efficient vehicles is not to save money. Although that would be nice. It would take years to pay off the price premium that fuel efficient cars incur.
The point of the higher mpg cars is to simply use less fuel and produce fewer emissions.
I bought a Q5 TDI because of the fantastic balance of great performance at reasonable fuel efficiency. And with the stupidly overtaxed price of diesel (don't get me started on that soapbox), it's never going to be a sound financial decision. Even so, diesel fuel is only marginally more expensive than the premium I'd be putting in any other high performance engine. I drive my TDI pretty hard and I'm averaging 28 with 50/50 city/hw driving. It's and easy 36 mpg long distance though.
The price premium and payoff time differs from vehicle to vehicle. Some cars don't have a huge mpg gap between their diesel and gas engined cars, or have a large price premium for the diesel, or both. Others don't.
In terms of luxury cars, it's a mixed bag. Let's look at the EPA mpgs for a few of them. For the Q5, let's look at the 3.0 vs the TDI, with the TDI's ~$2k upcharge
If the drivers get exactly the combined mpg over 12,000 miles a year, the two drivers will consume 571 and 444 gallons of gas and diesel, respectively. At the gas station by my house, premium is $3.99 and diesel is $4.09. The gas driver will spend $2278 a year on gas. The diesel driver will spend $1815 a year on gas, leaving a $463 delta. If both drivers keep their Q5s for 5 years, the diesel driver will have spent $2315 less in fuel costs than the gas driver, which covers the higher up front cost of the diesel model.
If you look at real world reported fuel economy on fuelly, diesel Q5 drivers are reporting a combined 30 mpg. With the gas V6 drivers (looking at 2013 and 2014 models, disregarding an anomalous 38mpg reading), they're reporting a combined 20 mpg. Using the same prices and driving distances for gas/diesel as above, the diesel driver saves $758 a year on fuel compared to his gas counterpart. With that delta, the diesel driver makes up the upfront price of the diesel in three years, right in line with a lease.
Same type of tradeoff with other cars. Several months ago, I ran the numbers for a MB E250 vs E350 and found a slightly quicker payoff with the diesel, at just a bit over 2.75 years.
...All that said, if I get a diesel, it's not primarily for fuel economy, although that certainly plays a part. Rather, it's the driving range and performance that I'm interested in.