Diesel vs Gas: The Pros and Cons of Diesel Vehicles

Diesel Engines Get Great MPG, But There Are Trade-Offs

Over the past 40 years, most automakers eventually offered diesel engines in the U.S. Though diesels are much rarer, found chiefly in pickup trucks and a handful of cars and SUVs.

Diesels have never been as popular in the U.S. as overseas, where high gasoline prices and tax incentives make them more economical choices. In the U.S., historically low gas prices have stunted demand for more fuel-efficient engines. In recent years, hybrid gas-electric and electric-only powertrains have pushed diesels further aside.

In addition, after Volkswagen was caught cheating on diesel emissions tests a few years back, that virtually killed demand for diesel-powered cars and SUVs in the U.S. Volkswagen and Audi, Mercedes-Benz, BMW, and other brands pulled most of them from the U.S. market.

Diesel engines, though, still have a loyal following, particularly among those who tow heavy boats and trailers, which explains why they remain popular in pickup trucks.

Fiat Chrysler Automobiles offers diesels in its Ram pickup line, Jeep Wrangler, and Ford and General Motors in their pickup trucks. Jaguar Land Rover is the only other manufacturer offering diesels in the U.S. for the 2020 model year.

Here are the key pros and cons of diesel engines compared to gas engines:

Pros of Diesel Engines

Better fuel economy

Diesel engines are 20% to 35% more efficient than conventional gasoline engines, so they wring more energy from the fuel and deliver more mpg.

For example, the EPA rated the 3.0-liter turbocharged diesel V6 engine in the Chevrolet Silverado at 25 combined mpg, compared to 19 mpg for the gas 5.3-liter V8. In the Ford F-150, a 3.0-liter turbodiesel gets 24 mpg, six more than a turbocharged gas 3.5-liter V6.

Heavy-duty pickups, such as the Silverado 2500 and 3500, Ford F-250 and F-350, and Ram 2500 and 3500, are not rated for fuel economy by the EPA. Still, owners say that the diesel versions get better fuel economy than their gas-driven brethren.

Why Are diesel vehicles more fuel-efficient than gas vehicles?

The fuel economy difference between gasoline and diesel engines is due to various factors, including diesel’s higher energy density and the increased efficiency of compression ignition vs. spark plug ignition.

It’s worth pointing out, however, that the higher fuel cost of diesel can offset the higher fuel efficiency of diesel cars.

More torque for towing

For many who tow, a diesel is the only option because it will produce more torque – the power needed to pull heavy loads such as big boats, horse trailers, and other vehicles.

Diesel engines produce large amounts of torque at low speeds and across a broad range of engine speeds, making them well-suited for towing, and they typically have greater towing capacity than gas engines.

For example, the Ford F-250 (with single rear wheels) can tow up to 15,000 pounds with a gas V8 engine but can tow 20,000 pounds with the 6.7-liter turbodiesel V8.

The Ram 2500 can tow up to 19,680 pounds with its 6.7-liter diesel engine, about 2,000 pounds more than the 6.4-liter V8. The difference is in the diesel’s massive amount of torque, 850 pound-feet, compared to 429.

Durability

Diesel engines typically last longer than gas engines, especially under grueling towing conditions, because diesels are usually built with stronger parts designed to withstand sustained hard use.

For this reason, diesel engines are often the preferred choice of fleet operators, such as delivery services and utilities. Those companies want to keep vehicles in service as long as they can – 300,000 miles or more – to reduce costs, and diesels are often regarded as a better long-term bet than gas engines.

Cleaner diesel vehicles are available

Modern diesel engines produce fewer pollutants thanks to better emissions systems and diesel fuel with lower sulfur content. Companies that make diesel vehicles and diesel fuel capitalized on those advances by touting their products as “clean diesel.”

Diesel engines in cars and light trucks must meet the exact emissions requirements as gas engines. Some scientific studies have shown that current diesels are as clean or cleaner than gas engines, except for the amount of nitrogen oxides they produce. Nitrogen oxides, or NOx, cause smog.

Cons of Diesel Engines

Higher initial cost

Diesels are more expensive than gas engines, sometimes by knee-buckling amounts.

On the Ford F-150, for example, a version with the 3.0-liter turbodiesel engine costs $4,000 more than one with the standard gas V6 and $3,000 more than one with a 5.0-liter gas V8.

On the heavy-duty Ram 2500, a 6.7-liter turbocharged Cummins diesel engine adds $9,300 to the bottom line.

Higher maintenance costs

Diesel engines usually have larger oil capacities than gas engines and may require more-expensive types of oil. For example, a Ford 6.2-liter gas V8 engine takes 7 quarts of oil, but its 6.7-liter diesel takes 13 quarts.

So that $29.99 oil change you see advertised probably won’t apply. For example, one Ford dealer in Florida advertised a $59.99 price for The Works (an oil change, tire rotation, and basic service package) for gas vehicles and $129.99 for F-Series pickups with a diesel V8.

When something breaks on a diesel engine, it’s likely to cost more to replace than on a gas engine because diesels use heavier-duty parts and have more elaborate and specialized emissions controls to reduce particulate emissions.

In addition, not every mechanic has the tools or training to work on diesels, so there may be fewer options for who can do the work.

Diesel Fuel Can be More Expensive and Harder to Find

Diesel fuel is easy to find along interstate highways. Still, not every station in the suburbs or a downtown metro area will have it because diesel requires a separate underground tank and a separate pump.

Refueling with diesel at some stations can require fueling up next to 18-wheelers or other large trucks.

In addition, when someone spills gasoline on the pavement at a station, most of it evaporates. Diesel fuel, however, is an oil, so it leaves a puddle or a greasy stain.

Not as useful in sporty cars

There’s a reason you don’t see diesel engines in many sports cars – diesel motors can’t match the performance of gas motors when you want a lightweight, high-revving, high-horsepower engine.

Because diesel engines have heavier blocks, lower RPM redlines, and favor torque for towing over horsepower for high-speed acceleration, they’re better in trucks than performance vehicles.

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        By the Numbers

        All About Diesel Engines

        Gas engine alternative

        From semi-trucks and heavy equipment to passenger cars and trucks, you can find millions of diesel-powered vehicles sharing the road with traditional gasoline engines. Since its invention in 1892 by Rudolf Diesel, the diesel engine has been a formidable alternative to the gas-powered engine.

        How much do you know about diesel engines? If your knowledge begins and ends with knowing that diesel fuel is sold at the gas station, we’ve got you covered. Read on to learn how diesel engines differ from gas engines, their advantages and disadvantages, and how to determine if a diesel-powered engine may be right for you.

        How a diesel engine works

        Like a gas-powered engine, a diesel engine is an internal combustion engine that uses a series of small explosions (combustions) to power the vehicle. What makes a diesel engine different is how the combustions occur. In a diesel engine, the air is compressed followed by fuel being injected into the cylinder. Because the air is so hot, the fuel ignites without the use of a spark plug as in the case of a gasoline engine.

        Here is what the four-stroke process looks like in a diesel engine:

        • Stroke 1 – Intake: Inlet valve opens to bring in air while pulling the piston down.
        • Stroke 2 – Compression: Inlet valve closes and the piston moves back up to compress the air, heating it up.
        • Stroke 3 – Combustion (power): When the piston is at the top, fuel is injected and ignites. The combustion pushes the piston back down.
        • Stroke 4 – Exhaust: Exhaust valve opens and the piston returns to the top, expelling exhaust out of the cylinder.

        The cycle repeats itself in each cylinder hundreds of times per minute to power the vehicle.

        Diesels on US roads

        In the US, diesel vehicles accounted for just 3% of total passenger auto sales in 2014. Medium and heavy-duty trucks made up the majority of sales while cars, SUVs and minivans tallied just 1.5% of sales 1 . With diesel fuel costing up to 50 cents more a gallon, most Americans are happy to stick with their gas-powered vehicle.

        While most Americans haven’t made the switch to diesel for their personal vehicle, diesel is the engine of choice for semi-trucks, construction equipment and buses thanks to diesel’s ability to efficiently move large loads at low speeds.

        Diesel is much more popular in Europe where close to half (49.5%) of all vehicles sold had a diesel engine in 2016. In some countries like Italy, Portugal and France, the percentage is even higher 2 . With its better fuel economy and lower CO2 emissions, diesels have long been favored in Europe.

        Advantages of diesel

        Better mileage – Improved fuel economy is a big selling point for diesel engines. Diesels can achieve 25-30% better mileage than a gas engine due to the higher efficiency of diesel fuel, while the direct fuel injection during the combustion process wastes little fuel.

        More power – More torque and a better power-to-weight ratio allows diesel engines to handle heavy loads, which explains why it’s used in big rigs and heavy equipment. The improved towing power is why some truck buyers look to diesel.

        Lower emissions – Modern diesel engines emit lower levels of CO2 and carbon monoxide than gas engines.

        Less maintenance – With no spark plugs and less stress, diesel engines can run longer before requiring maintenance.

        Long lasting – Thanks to higher compression, the parts of a diesel engine suffer less wear and tear than a gas-powered engine. It isn’t uncommon to hear of diesel engines making it to the 500,000 mile mark.

        Safer – Diesel fuel is less volatile and the vapor is not as explosive as gasoline. This reduces the chance of the fuel igniting and causing a vehicle fire.

        Disadvantages of diesel

        Higher fuel costs – The higher cost of diesel fuel has been a hurdle to diesel vehicles being widely accepted. Diesel fuel can be up to 50 cents more per gallon than regular unleaded fuel.

        More expensive purchase price – A vehicle with a diesel engine is typically more expensive to purchase than its gasoline counterpart. Built to handle more punishment, the heavy-duty parts add to the sticker price.

        Noisier – While modern diesels aren’t the noisy engines of years past, they still are noisier than gas engines. Listen to both vehicles side-by-side to see if the noise level is a deal breaker for you.

        Pollution – Despite advances, diesel fuel still produces some harmful emissions like nitrous oxide and soot. However, today’s low-sulfur diesel fuel has greatly reduced these emissions.

        Cold starts – Diesels can have difficulty starting in cold temperatures since they don’t have spark plugs and instead ignite spontaneously. When it’s cold, the air may not be hot enough to ignite the fuel. Devices like heating elements and block heaters are used to counter the problem.

        Is a diesel right for me?

        To determine if a diesel vehicle is right for you, you need to examine your driving habits. If you drive a lot of highway miles, a diesel could help you save money in fuel costs. Diesels typically deliver better highway mileage numbers than city driving. However, if you don’t put a lot of miles on your vehicle, it will be difficult to make up the higher purchase price of a diesel in gas savings.

        If you find yourself towing a boat, camper or trailer on a regular basis, diesel’s low end power could be right for you. The additional torque can help you efficiently haul a bigger load. Definitely take a close look at diesel if you’ll be doing a lot of your driving in the mountains. Again, diesel’s low end power is a big help on those steep climbs.

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