New emissions standards and technological advances are revising old assumptions about engine choices.

With fuel prices reaching record highs, companies are taking a close look at every option that can give their companies an edge in reducing fleet costs.

This includes examining the advantages of gasoline vs. diesel engines with new scrutiny. The increasing cost of diesel engines and the technological improvements in gasoline engines and vehicle weight are all factors causing fleet managers to reconsider their options.

The conventional wisdom has been that, while diesel engines cost several thousand dollars more up front, their better fuel economy, longer lifecycle and simpler maintenance requirements have made them a more economical choice over time, especially if your fleet runs at least 20,000 to 26,000 miles a year.

However, as diesel engine manufacturers have hustled to meet new government-mandated emissions standards, first for 2004 and now for 2007, they have had to increase prices, widening the upfront cost between diesel and gasoline engines to $7,000 or more, while reducing diesel’s long-term cost advantage.

At the same time, gasoline-engine technology has improved rapidly. General Motors’ new 4.8L and 6.0L Vortec engines are prime examples: Their fuel economy is 7% to 10% better than previous models, while such things as 7,500-mile oil-change intervals, a coolant life of 150,000 miles and major-maintenance intervals of 100,000 miles have lowered maintenance costs. Durability also has been enhanced, giving gasoline engines an effective lifecycle of 200,000 miles or more.

Furthermore, gas engines are certified as “federal clean fuel” engines in all 50 states, while a number of diesel engines fall short of that, particularly in California. At the same time, gas engines are able to meet North American emission standards without the use of an Exhaust Gas Recirculation System, thereby reducing engine complexity and improving reliability.

For snack and bakery fleets, weight is also an important consideration. Because their cargo is more bulk than heft, many of these fleets can run with trucks at 10,000 lbs. GWVR (gross vehicle weight rating) or lower. This allows fleets to avoid the costs of medical tests and other driver requirements that come into effect for heavier GVWR classes.

For example, the aforementioned 6.0L Vortec gas engine is 637 lbs. lighter than a comparable ISB6 Cummins diesel. Gasoline fuel also weighs less than diesel. This lets a gasoline-driven truck haul more cargo at the same GVWR.

That said, some excellent new diesel choices are coming to the forefront as well, such as Navistar International’s all-new VT 275 engine that can generate up to 200 horsepower and 444 ft.-lbs. of torque with exceptional efficiency. It has a 250,000-mile lifecycle design and also simplifies routine maintenance with mechanic-friendly features such as easily accessible cartridge-style fuel and oil filters.

So while the gas vs. diesel debate isn’t settled, ever-changing engine technology arguably can change the cost equation for a particular fleet, depending on its specific capabilities and needs. More and more, fleets are relying on truck manufacturers to help them sort out these changing equations to arrive at a solution that’s best for them.