At first glance, gasoline and diesel engines are incredibly similar. Both take fuel, make small explosions and move cars. While both motors have similar designs and do the same basic thing, there are a few key differences between the two.
A diesel engine takes a very simple and direct approach to internal combustion. Its design involves compressing the air as much as 2-1/2 times more than a gasoline engine. Compression causes heat. So when the fuel is delivered, through a high-pressure fuel injection system, to the compressed air, the heat, which can reach as high as 1,000 degrees Fahrenheit thanks to glow plugs, causes the fuel-air mixture to explode all by itself. A gasoline engine needs spark plugs (one for each cylinder) to make that happen.
Diesel Heat Equals Efficiency
Ever wonder why a diesel engine gets better fuel economy than a gasoline engine? All that compression and heat causes the fuel to burn more completely, meaning more energy is released from each drop. And, you’ve probably heard that you burn more gasoline idling, right? In a diesel engine, the less power you’re trying to generate, the less fuel it requires.
Diesel Fuel Makes a Difference
Diesel fuel is different from gasoline. For one, it’s less refined, and second, it has a higher energy density than gasoline — meaning more energy per molecule. Combine that with the efficiency of the engine and you can see how a gallon of diesel can get you farther down the road than a gallon of gas.
So What Kind of Car Should You Buy?
For all of the upsides to diesels in terms of fuel economy, maintenance — no spark plugs means no tuneups — and longevity (not only are diesel engines tougher, but their components don’t come into contact with one another as much as those in gasoline engines), there are drawbacks.
Diesel Engine Downsides
The first is initial cost. That rugged construction comes at a price, as diesel cars and trucks are generally about 20 percent more than similar gasoline-powered models.
Next is the cost of diesel fuel itself. It tends to be more pricey than regular gas. That could add up over time, especially if you’re doing a lot of traveling.
Finally, the diesel field is shrinking. Some manufacturers, responding to ever-tightening emissions requirements in Europe and elsewhere, are abandoning it. Unless you’re buying a full-size, and most often a heavy-duty, truck, diesel-powered vehicles are growing scarce.
You need to define exactly what kind of vehicle is right for you. Crunching the numbers on purchase price and fuel costs, and how much they’re offset by fuel economy and overall longevity, will give you a better idea of if a diesel outweighs a vehicle that uses gasoline.
Check out all the fuel and emission system parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on the pros and cons of diesel fuel, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photo courtesy of Wikimedia Commons.
Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of MikeHagertyCars.com, and contributes car reviews to the Los Altos Town Crier and losaltosonline.com. Previous outlets have included KFBK and KFBK.com in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and BBCCars.com.