Diesel vs. Hybrid: A Comparison for Car Shoppers

• We examine diesel vs. hybrid technology.
• Hybrid is good for low-mileage motorists.
• Diesel is better for long distance drivers.

If you’re looking for a fuel-efficient new ride, it’s likely that you’ve spent some time considering hybrids and diesels. Both powertrains are good on gas, widely available and easy to maintain. So what’s the difference? It might surprise you to learn there are quite a few differences, and depending on your driving style, one engine might be a far better choice than the other.

First, a little background: The term “hybrid” is broadly defined as the use of two powertrains to move a vehicle, but the term is typically used to reference cars with gasoline and electric motors. While it’s possible to recharge some hybrid cars (such as the Chevrolet Volt) by plugging them in to an electrical outlet, most hybrid cars (such as the Toyota Prius, Ford Fusion Hybrid and Honda Insight) use the combustion engine and a process called “regenerative braking” to restore battery power.

As a result of regenerative braking, which converts kinetic energy from stopping into battery power, hybrid cars are a good choice for drivers who live in big cities or do lots of stop-and-go driving. While traditional gas-powered cars tend to return better fuel economy on the highway due to a continuous engine speed, regenerative braking boosts hybrid gas mileage around town by charging the battery as the car slows down. Several hybrids, including the Ford Fusion, Toyota Camry and Toyota Prius, actually offer better fuel economy in the city than on the highway because of this feature.

Due to their battery technology, hybrids are also a good choice for in-town drivers who travel shorter distances. Because the battery is essential for the powertrain in most hybrid vehicles, battery failure immobilizes the vehicle. (A replacement can cost as much as $4,000.) While this is unlikely to happen within the first 100,000 miles, long-distance drivers could be looking at a costly battery replacement every few years. Meanwhile, city-dwelling drivers who limit their driving to less than 15,000 miles a year might not have to replace the hybrid battery for the life of the car.

Diesel engines, meanwhile, are more similar to traditional gasoline powerplants. Drivers who choose a diesel car, such as the Volkswagen Jetta TDI, Mercedes E350 BlueTEC or BMW X5 xDrive35d, likely won’t notice many differences between their vehicle and a gas-powered car–except at the pump, where they may have to pay a little extra for diesel fuel. Indeed, much of the difference between diesel and gas is under the hood, where diesels eschew spark plugs to burn fuel far more efficiently than gas-powered cars.

Due to their increased efficiency, diesels allow drivers to keep engine speeds lower, which results in a much improved fuel economy compared to traditional gas-powered cars. The result is mildly improved fuel economy around town but vastly increased mileage on the highway, where the engine can run more efficiently for longer periods of time. As an example, the Audi A3‘s 2.0-liter diesel engine records a gain of eight miles per gallon over its gas counterpart in the city but a 14-mpg improvement in highway driving. Thus, diesel tends to be a better choice for motorists who do a lot of highway driving, since the powertrain will continue to pay off as miles are tacked on. Diesel also requires slightly less long-term upkeep than gas engines, since it doesn’t have spark plugs that need changing every 100,000 miles.

Overall, both diesel and hybrid likely will cut down your fuel bills. But depending on how you use your vehicle, one might merit more serious consideration than the other.

What it means to you: Drivers comparing diesel vs. hybrid should analyze their driving style and pick which technology suits them best.