There have been plenty of diesel versus gas arguments. You pay more at the dealership for diesel, yet the range on each tank is better. But prices at the pump fluctuate with diesel, yet diesel engines excel at hard work and often last longer, so it's worth it. Now there is a study that shows that, despite the costs that are associated with diesel engines, diesel-powered vehicles saved owners money -- and a significant amount at that.

The data was collected by the University of Michigan Transportation Research Institute, and it shows that owners saved $2000 to $6000 in total ownership costs during a 3-5-year period when compared with similar gasoline vehicles. The study, called "Total Cost of Ownership: A Gas Versus Diesel Comparison," was conducted for Robert Bosch LLC. The results were recently released at the 2013 Alternative Clean Transportation Expo in Washington, D.C.

According to the study, "Overall, the results of our analyses show that diesel vehicles provide owners with a TCO (total cost of ownership) that is less than that of the gas versions of the same vehicles. The estimates of savings for three and five years of ownership vary from a low of $67 in three years to a high of $15,619 in five years, but most of the savings are in the $2000 to $6000 range, which also include the extra cost that is usually added to the diesel version of a vehicle."

"These new findings that clean diesel vehicles are a more cost-effective investment for car owners reinforces what auto analysts and other comparative studies have determined in recent years," explains Allen Schaeffer, executive director of the Diesel Technology Forum. "The significant savings diesel owners experience compared to gas car owners highlights another major reason why clean diesel vehicles sales will increase significantly throughout the U.S. in the coming years. He continues, "Fuel efficiency has always been a major attraction of clean diesel vehicles. Because diesels are 20 to 40 more fuel efficient than gas cars, drivers save money with diesels even when diesel fuel prices are slightly higher than gas prices.

"The findings in this study will also be helpful to car buyers as they research their next vehicle purchase. This is an exciting time for diesel vehicles, as the number of diesels is expected to more than double in the next two years. This will give drivers a broad selection of vehicles to fit their individual driving needs. In addition, as the U.S. moves to the increase fuel standards to 54.5 mpg by 2025, drivers will become more aware of the advantages diesels have over other vehicles in many important areas."

Some highlights from the study: TCO: In the study's 3-year time frame, mass-market passenger-car diesels are estimated to save owners significant money: $3128 with the VW Jetta, $3389 with the Jetta Sportwagen, and $5013 with the Golf.

In the luxury segment, the diesel Mercedes-Benz E-Class ($4175), GL-Class ($13,514), M-Class ($3063), R-Class ($5951), and VW Touareg ($7819) save owners money in the same timeframe. That GL-Class savings is shocking.

Fuel Efficiency: As you would expect, all the diesel vehicles had better mpg than the gasoline versions. The difference was 8 to 44 percent higher mpg with the diesels.

Fuel Costs: In all cases, the diesels had lower fuel costs than the comparable gas versions, with 11 of the 12 vehicles showing double-digit reductions in fuel costs -- those ranged from 10 to 29 percent.

The study also showed that when looking at the trends over 5 years, they stay similar to the 3-year comparisons. Estimated fuel costs for diesel vehicles were still less than those of comparable gas versions. Because diesel prices began to increase around 2005, the percentage difference decreased in some cases when looking at the reduction of costs from gas to diesel.

Depreciation: Eleven of the 12 diesel vehicles held their value better than comparable gas vehicles over the 3-year time frame. Eight of the vehicles showing double-digit savings, ranging from 17 to 46 percent.

Nine of the 10 diesel vehicles hold their value better than comparable gas vehicles over the 5-year time frame. Here, five vehicles showed double-digit percentage savings ranging from 10 to 39 percent.

The report analyzed the Total Cost of Ownership (TCO) for clean diesel vehicles and comparing their TCO to their gas vehicle counterparts. The study developed 3-and 5-year cost estimates of depreciation by modeling used vehicle auction data and fuel costs by modeling government data. The study also combined these estimates with 3- and 5-year estimates for repairs, fees and taxes, insurance, and maintenance from an outside data source.

Motor Trend has had a similar experience with diesel versus gas long-term vehicles, specifically with a gas and a diesel 2012 Volkswagen Passat. As Mike Febbo explains, "We racked up a total of 25,332 miles on the TDI SE and 25,521 on the 2.5-liter SEL. TDI fans won't be surprised to read that our TDI beat the EPA mpg ratings of 30 city/40 highway/34 combined, returning 39.4 mpg combined. On a few road trips, the diesel Passat achieved close to 50 mpg.

"One of my own trips involved filling up in Huntington Beach, driving to Las Vegas, driving around Las Vegas for three days and then driving back to Huntington Beach. I filled up at the gas station with 694 miles on the trip odometer and the tank required 16.5 gallons—that's 42 mpg.

"At the end of the year, the TDI drank a total of $2628.75 worth of diesel, which probably doesn't mean much until you consider the 2.5-liter required $3995.21 for virtually the same number of miles. Volkswagen doesn't build gas- and diesel-powered cars exactly apples-to-apples, but with fuel costs alone, the TDI would pay for itself in under 60,000 miles."

Source: Diesel Technology Forum, Motor Trend