What Makes a Diesel Truck Different From a Gasoline Truck?

Although gasoline engines in the US are more popular, a diesel truck makes a lot of sense. Diesel trucks can tow and haul more while burning less fuel. Diesel truck engines also last much longer than gasoline ones. And diesel trucks can do all this because of what makes them different from gasoline trucks.

Diesel vs. gasoline: how they work

What makes diesel trucks different from gas trucks ultimately comes down to the fuel. Because while both diesel and gasoline come from crude oil, they have very different properties. This also changes how each truck burns its fuel.

Both diesel and gasoline truck ignition start the same. Valves open to let air in, fuel gets injected, and a piston rises up to compress the air-fuel mixture. It’s at this point where the differences between gasoline and diesel come into play. Compressing the air and fuel heats things up. But not enough for a gasoline engine: it needs a spark plug to ignite the air-fuel mixture and produce power. Diesel, on the other hand, can auto-ignite just because of the compression.

Not only does this eliminate the need for a spark plug, it also makes it more energy-efficient. This is why diesels get better fuel economy. This also explains why diesel engines are so heavily-built compared to gasoline engines, and why they last longer. A diesel engine’s parts have to deal with a lot more pressure. As PickupTrucks.com explains, they’re built tougher, which makes them last.

Why diesel trucks have two batteries, lower redlines, and more torque

While compression-ignition is good for fuel efficiency, it does require a bit more equipment. Sometimes, outside temperatures are low enough that the compression isn’t enough to ignite the diesel. That’s why modern diesel engines have glow plugs—basically mini-space heaters or toasters. These glow plugs and the diesel engine’s high compression are why diesel trucks have two batteries, explains Parkside Motors. One battery alone wouldn’t provide enough juice for the starter motor or the plugs.

A diesel truck’s design, reports Car Throttle, also explains why diesel engines don’t rev as high as gas ones. The pistons have to travel farther, which limits speed. This is also why diesel engines don’t make as much horsepower as gasoline ones. But diesel engines have gas engines beat when it comes to torque.

This comes down to both the diesel fuel itself, and the engine’s design. Diesel fuel is more energy-dense than gasoline, so it produces a bigger boom when it ignites. This means more pressure on the piston, which equals more torque. But today’s diesel engines can produce even more torque with the help of turbocharging.

Why and how turbos help diesel and gasoline trucks

Turbos do the same job in both gasoline and diesel trucks. They use the energy of exhaust gas to compress and shove more air into the cylinder. In both types of engines, this results in more horsepower and more torque. As Diesel World explains, this helped diesel engines keep up with gasoline engines. And even, as Car Throttle explains, in some cases overtake them.

Because diesel engines are built tougher, they can handle higher boost pressures. Not only does this make for even more horsepower and torque, it’s actually more efficient for the engine.

But there is a problem with putting a turbo on a diesel engine. And it’s an issue that’s built-in to the diesel engine’s design.

Why diesels need diesel exhaust fluid

Although diesel engines produce less of certain pollutants than gasoline engines, they also produce more of others. Especially soot, NOx compounds, and in the days before low-sulfur diesel, SOx emissions. SOx compounds dissolve in rainwater to produce acid rain. NOx compounds are responsible for the thick haze that choked LA and other cities until the EPA and CARB stepped in. And soot from rolling coal continues to be a problem.

Unfortunately, soot and NOx production are tied into how diesel engines work: compression ignition. Fortunately, there are ways to deal with these emissions. Soot gets trapped in modern diesels’ particulate filters. And for NOx, there’s DEF, which is usually a mix of water and urea. After passing through the particular filter, DEF is sprayed into the exhaust gas stream. There it reacts with the harmful NOx compounds and air to produce safer emissions.

But soot doesn’t just show up in the exhaust. For it to be there, it also needs to be in the engine. And that’s where diesel truck oil comes into play.

Diesels differ from gasoline trucks when it comes to oil

Diesel trucks depend on oil even more than gasoline trucks. Truck oils already have more detergents and additives than car oils, but diesel oil goes even further.

2020 Chevrolet Silverado Diesel
2020 Chevrolet Silverado Diesel | Chevrolet

Like gasoline trucks, diesel trucks use oil to keep their engines cool, clean and lubricated. However, as Car Talk explains, because of all the soot and compression, diesels need more oil to do the same job. The extra oil dilutes the contaminants enough for the oil to still do its job. Nevertheless, diesel trucks still require oil changes more frequently than gasoline trucks, especially if they’re used for towing.

Diesels have their own pros and cons. But that’s because of what makes diesel trucks so different from gas trucks.