Diesel vs. Gasoline? Today, the Answer’s Less Clear

Diesel vs. gasoline? This is a question that light-truck buyers have faced almost since diesels became widely available back in the 1980s. Diesels earned a reputation for durability, long life, and often — but not always — high fuel economy.  

One engine, the Cummins Turbo Diesel from Dodge and Ram, developed a cult following that spawned a website and regular festivals. Ford’s Power Stroke and General Motors’ Duramax diesels found their own followers, and it got to where the “real man” would spec a diesel whether he needed it or not.  

For fleet operators, the need centered on the operating savings to pay off the diesel’s price premium, both at purchasing time and at the pump, in a reasonable amount of time — maybe two or three years.  

That’s not easy to do anymore. Today the sales trend is toward gas, according to executives at the Big Three truck builders. Ford’s Nathan Oscarson, Ram’s Dave Sowers, and GM’s Dan Tigges all observe that the price premium for a diesel has gone up since exhaust-emissions limits have grown more stringent.  

Gas Trend for Commercial Trucks

Developing exhaust-gas recirculation systems and exhaust aftertreatment equipment has been tremendously costly and the equipment is expensive. All that must be passed on to customers. The cost differential for a larger diesel pickup is $8,000 to $11,000 — though a smaller diesel in a ½-ton pickup can be far less.  

Meanwhile, a gallon of diesel fuel is usually $1 or so more than gasoline, although per-gallon prices of both plunged this year when a production war between Saudi Arabia and Russia drove down petroleum prices and the coronavirus-caused economic slump cut demand.  

Years before, the builders saw the trend toward gasoline coming and each fielded larger gasoline engines to supplement diesels. The latest is Ford’s 7.3L gas V-8, which is becoming popular in Super Duty pickups and larger cab-chassis models, Oscarson says.  

GM’s new 6.6L gas V-8 has “amazing performance” and sales are climbing, Tigges says. And Ram’s 6.4L Hemi gasoline V-8, introduced several years earlier, has caught on in many applications, says Sowers.  

The new gas engines not only do the hauling job, but are lasting longer, routinely running 200,000 miles and more with few repairs. And direct-injection fuel systems have reduced fuel use while working on the road or at idle (though in some cases direct injection complicates conversions to comparatively cheap propane or natural gas — generally another advantage of gasoline engines).  

All of the Big Three’s large gasoline engines run on 87-octane fuel, even with high compression ratios that bring greater fuel efficiency but traditionally demanded premium. Now, knock sensors allow an engine’s electronic ignition to constantly adjust spark and timing. 

Gasoline engines cost less to maintain because they’re easier to work on and consume less motor oil at drain time, Ford’s Oscarson noted. And their exhaust systems need only catalytic converters. Gasoline needs no additives to keep flowing in very cold weather, though like any fuel, water intrusion can cause headaches.  

On the other hand, diesel fuel should either be of the premium variety in freezing and subzero temperatures or be treated with additives to avoid clouding and waxing that can plug filters and starve engines, and if the wax crystals get through, blow injectors. Complex diesel aftertreatment systems can be costly to maintain and repair and require diesel exhaust fluid at varying intervals.  

Diesels still have longer lives due to their heavy construction, something needed to survive the pounding of very high cylinder compression.  

New Thresholds for Fleet Needs

If operators know how to care for them, diesels are still the way to go where mileage is high and heavy loads are frequently carried or pulled. Thus the heavier the truck, the more likely it is to get a diesel, the Big Three execs say.  

And the fewer the miles and the lighter the loads, the better a gasoline engine becomes, especially if a truck’s engine is shut off much of the time. Fifteen or so years ago, the operating threshold for choosing a diesel was 30,000 miles a year. Above that, a diesel began earning its keep by cutting fuel and maintenance bills.  

Now that threshold might be 40,000 miles and maybe more. A buyer should do an analysis to see where the numbers fall in his or her operation. Simply balance diesel’s upfront premium against any fuel economy gain, then factor in the difference between the cost of gasoline and diesel. The dollars-and-cents answer should be clear.  

But wanting something can be more important than needing it. So, the builders report that retail customers are more likely to spec a diesel than fleet managers. Hey, it’s a free country.