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The Gas Versus Diesel Decision

July 1, 2008
If you are shopping for a new truck for your company's delivery fleet, you will learn that gasoline- and diesel-powered engines each have their own distinct advantages.
COMPARING GASOLINE AND DIESEL PRICESGASOLINE (CENTS PER GALLON)DIESEL FUEL (CENTS PER GALLON)6/16/08Change from6/16/08Change from Price Week Ago Year Ago Price Week Ago Year Ago U.S. 408.2 4.3 107.3 U.S. 469.2 0 188.7 East Coast 405.2 3.3 107.6 East Coast 475.2 0.9 195.2 New England 413.1 4.2 111.1 New England 485.3 1.9 197.6 Central Atlantic 410.3 4.5 108.9 Central Atlantic 487.4 -0.5 200.5 Lower Atlantic 399 2.1 105.6 Lower Atlantic 469 1.3 192.6 Midwest 399.7 1.5 101.3 Midwest 461.8 0.3 184.4 Gulf Coast 393.7 2.8 103.4 Gulf Coast 465.6 -0.2 190.3 Rocky Mountain 399.4 5.3 81.3 Rocky Mountain 468.5 -1.3 177.8 West Coast 445.2 12.7 126.4 West Coast 485.2 -2.2 189.4 California 458.8 15.5 135.2 California 496.9 -2.3 193.6 Source: Energy Information Agency (

One common question truck dealers often get is, “Which engine is best — gasoline or diesel?” Making that choice is easier when you consider how the truck will be used, its fuel mileage, how much it will cost to operate, and the acceleration and load-handling characteristics you need.

If you are looking for quick acceleration, a gasoline engine might be the better choice. That's because acceleration is a function of engine horsepower, which is usually higher in a gas engine than with a diesel of similar size.

While a gasoline engine has the horsepower to provide quick acceleration when a truck is lightly loaded, the same truck-engine combination will accelerate more slowly with a heavy load. The torque of an engine enables it to move a heavy load. A similarly sized diesel engine generates more torque.

According to Dennis O'Connor of Christopher Trucks, load-pulling torque is a hallmark of the diesel. Diesels are also known for their fuel efficiency, which he says is the main reason more than 95 percent of the light trucks sold at the Greenville, S.C., dealership have diesel engines. The full-service commercial dealer sells and services numerous makes and models of trucks, including Freightliner, Sterling and Isuzu commercial utility vehicles.

In a recent independent test of four gasoline-powered and four diesel-powered light trucks conducted by Automotive Marketing Consultants Inc. (AMCI), Marina Del Rey, Calif., the diesel-powered Freightliner Sprinter 2500 commercial utility vehicle delivered 51.8 percent better fuel mileage at 20.2 miles-per-gallon (mpg) than the gasoline-powered Ford E250 van at 13.3 mpg. The average fuel mileage for the four diesel-powered vehicles in the test was 18.15 mpg, compared to 14.2 mpg for the four gasoline-powered vehicles — a 27.8 percent advantage to diesel. Averages were based on 680 miles driven for vehicles loaded with 1,500 pounds for half the test distance.

Depending on how a vehicle is used, O'Connor of Christopher Trucks says he routinely sees diesel-powered trucks delivering real-world fuel mileage 30 percent better than gasoline-powered trucks. He recommends gasoline engines when travel is less than 30,000 miles per year, and says diesel engines are better for mileages above 30,000.

As fuel prices climb, diesel has become more expensive than gasoline. According to data published in mid-June by the U.S. Energy Information Agency (EIA) at, the average price of a gallon of gasoline was at $4.08, 15 percent lower than a gallon of diesel at $4.69. Check out the chart on page 25 for more detail.

The price of diesel fuel is higher than gasoline due to several factors, EIA reports. Higher demand globally is putting more pressure on limited refining capacity, and it's more expensive to produce and distribute the new low-sulfur-content diesel. (Low-sulfur diesel helps reduce exhaust pollution.) In addition, the federal excise tax on a gallon of diesel is six cents higher than on gasoline.

But while the price for diesel is about 15 percent higher than gasoline, the higher purchase price can be more than offset by the higher fuel mileage a diesel delivers. You must also evaluate costs for maintenance like changing the engine oil and oil filter for the different types of engines. Several factors to consider are the frequency of the service and its cost. According to O'Connor of Christopher Trucks, gasoline and diesel engines sold by one truck-maker usually have the same mileage requirements for oil changes. Typically, truck makers recommend oil changes every 5,000 or 7,500 miles. For example, the recommended mileage to change engine oil and filter for a 2008 Ford Econoline cargo van with a diesel or gasoline engine is every 7,500 miles, while the oil-change recommendation for both types of engines in the 2008 Freightliner Sprinter is every 10,000 miles.

In addition to the frequency of recommended engine-maintenance intervals, owners should consider the fact that oil changes will cost more for diesel engines. Diesels also have special devices called fuel-water separators that must be serviced regularly. Ultimately, O'Connor estimates an oil and filter service for a diesel engine may cost $175, while the same maintenance for a gasoline engine may cost less than $30. How a truck will be used, mileage and how often the engine needs service are all factors to consider when choosing the engine for your next truck.

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