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Diesel vs. Gas: What’s the Difference?

It’s a perennial question among truck lovers and fleet managers, to go with gas or diesel? We breakdown the pros and cons in the diesel versus gas debate.

How the Engines Work Differently

Both diesel and gasoline engines are ICEs (internal combustion engines) that use a mixture of fuel and air to create an explosion in order to move a piston. But how they mix that air and fuel and how that explosion is initiated differs between the two. In a gas engine the air and fuel are mixed and then injected into the cylinder where it’s ignited by a spark plug. A diesel engine on the other hand, compresses air and then injects the fuel. The hot compressed air and fuel spontaneously combust thereby moving the piston.

How the Fuels Differ

Gas station at dusk

Diesel is less refined and therefore more energy dense than gasoline. Because of this, diesel provides better fuel efficiency, and this in turn is largely why its favored for use in large trucks and heavy equipment. The other reason is torque.

It’s widely known that when you want to tow or haul serious tonnage you want a diesel doing the work. But why? Because the higher compression ratio and longer piston stroke of a diesel engine produces more power at lower rpms.

Mileage: Winner Diesel

Since diesel provides literally more bang for the proverbial dollar it’s the more economical choice, especially considering gas and diesel now sell for roughly the same per gallon (market fluctuations not withstanding). And because vehicles operate more efficiently on the highway, if you’re looking for a longhaul fuel, you stand to save up to 30% in fuel costs by opting for diesel over gas. 

Emissions: Tie

Cars and trucks driving on busy freeway

This one is tricky. Diesel doesn’t produce as much carbon monoxide or carbon dioxide (which means it’s releasing fewer greenhouse gases), but instead it produces more emissions like soot, nitrogen oxide, and sulfur dioxide. Such emissions raise cancer rates, increase smog, and produce acid rain. Because of these dirty emissions, diesel engines usually have catalytic converters and other exhaust filtration systems which reduce the amount of particulate released.

Also Read: Emissions Testing: Everything You Need to Know

Maintenance: Winner Gas, Sort Of…

Although diesel will save you money at the pump, it will cost you more once you’ve taken your vehicle in for service. Even a simple oil change can cost anywhere from 2 to 4 times more. There are three factors at work here. First, a diesel engine requires more oil than a gasoline engine, usually up to 40% more. Second, because diesels run dirtier, they need more frequent oil changes than gas engines. Third, they require specialized diesel oil that differs from the more common gas engine oils. Add the associated cost of a diesel, from the exhaust systems and turbochargers to the increased frequency of regular maintenance and servicing it can get costly.

Yet, the near-term cost of maintaining a diesel engine might not outweigh the long-term savings. Which gets us to our next point.

Value: Tie

Man fueling up his vehicle at the pump

If you’ve ever been in the market for a heavy duty truck you will have noticed that the diesel version of the same truck costs more, sometimes considerably so. And in addition to the increased cost of oil changes, diesel engines are also often more expensive to fix, between the weightier components and the additional exhaust systems. Once balanced against diesel’s fuel savings all of these extra expenses look to easily tip the scales in favor of a gas engine.

But not so fast. Diesel engines tend to last longer than gas engines, experiencing a higher quality of life beyond 100,000 miles. So, if you plan on keeping your diesel truck for the length of its life, you’ll be best positioned to reap those rewards since the fuel savings really start to add up at those higher mileages. And even if you find yourself needing to sell your truck, it’d be good to know that diesels tend to retain their value and command more on the secondary market (though this is partly related to their higher initial cost).

Drum Roll… The Winner Is… Gas!… Or Diesel!… Really, it Depends

Whether to go diesel or gas really hangs on what you need your vehicle to do. If you plan on hauling heavy loads up steep mountain passes, you’re probably right to buy a diesel. But if you’re needing a more conventional vehicle intended for more conventional driving, there’s little reason to go with the extra expense of a diesel just to save on fuel.

Diesel may be better for addressing climate change and boasts hefty tow numbers but I know a few companies that appear intent on making such arguments obsolete.

What’s your feeling on diesel versus gas? Share your thoughts in the comments.

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Chris Kaiser

With two decades of writing experience and five years of creating advertising materials for car dealerships across the U.S., Chris Kaiser explores and documents the car world’s latest innovations, unique subcultures, and era-defining classics. Armed with a Master's Degree in English from the University of South Dakota, Chris left an academic career to return to writing full-time. He is passionate about covering all aspects of the continuing evolution of personal transportation, but he specializes in automotive history, industry news, and car buying advice.

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