Fuel economy is the primary motivation for buying a clean diesel, and as we outlined in our previous 2014 Volkswagen Passat TDI long-term update, there are plenty of engine technology advancements that have made modern diesels virtually indistinguishable from their gasoline-powered counterparts. Does that mean clean diesels always match their claimed fuel economy numbers? We recorded real-world figures to find out.

Real-World Efficiency

As we've outlined in our introductory 2014 Volkswagen Passat TDI long-term article, this German sedan is rated at 31 miles per gallon in the city and 43 mpg on the highway with the 6-speed manual transmission and an even 30 mpg city/40 mpg hwy when equipped with the dual-clutch automatic transmission. It's easy to dismiss official fuel economy ratings as unrealistic, especially since some manufacturers have endured public criticism after being exposed for having exaggerated mpg ratings, so we recorded the results of our real-world driving and compared them against the 2014 Volkswagen Passat TDI's Environmental Protection Agency (EPA) estimates.

We've been piling on the miles so far in our 2 months with the Passat, putting over 5,300 clicks on the odometer under a variety of driving conditions from slow city crawls to constant-speed highway runs. During that time, we've pulled an average of 35.6 mpg, which lands the Passat's real-world numbers slightly above its official combined EPA estimate of 34 mpg. More impressive than that number is the fact that we haven't been driving our TDI particularly gently but rather in a normal (and sometimes brisk) manner that enables us to get from point A to point B without holding up traffic. Conveniently enough, we've also managed to average 598 miles from the car's 18.5-gallon tank before refueling, making visits to the pump few and far between.

When cruising at 70 miles per hour or so, the indicated instant fuel economy has tended to creep into the high 40s, suggesting that the Passat TDI's tall sixth gear and favorable aerodynamic drag coefficient of 0.29 might help it perform considerably better on a road trip. That info makes us eager to plan our next excursion.

The Cost of Entry

Real-world fuel economy in the mid-30-mpg range is certainly attractive for a midsized sedan, but that number becomes less attractive when the cost of entry is high or diesel prices soar above those for standard gasoline. As for the Passat's pricing structure, it's hard to compare apples to oranges because its gasoline versions come equipped with different trim levels. As such, the TDI lies smack in the middle of the 4-model Passat lineup: The 1.8T model starts at $20,995, while the middle-range Sport Edition 1.8T's $26,475 starting price barely undercuts the TDI's by $200. The top-end gasoline-powered V6 comes in at $29,665.

As for the cost of filling up, current market trends suggest that it's a good time to go clean diesel: We've consistently seen diesel priced anywhere between 10 and 40 cents cheaper per gallon compared to regular unleaded prices, which makes the elevated mpg figures translate to even greater long-term savings.

What Lies Ahead

Based on our time with the Volkswagen Passat TDI so far, we've been pleasantly surprised at its ability to deliver decent performance while pulling exceptional fuel economy figures. In our remaining months with the car, we're hoping to explore how well our silver sedan can do on long-distance drives and how fuel economy is affected by exclusively driving in the city.

Stay tuned to see how the Passat TDI delivers on both fronts.

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Basem Wasef is an automotive journalist, author, and photographer with two coffee table books under his belt, and is a regular contributor to Popular Mechanics, Robb Report, and Maxim among others. When Basem isn't traveling the globe testing vehicles, he enjoys calling Los Angeles home.

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