Not every fuel-saving technology is a complete reinvention of the traditional internal combustion engine. Hybrid, electric, and fuel-cell cars have the potential to change the way we power vehicles in the U.S. But there have been many smaller innovations that are saving fuel right now.

Read below for details on engine upgrades; transmission advances; and weight reduction, tire tweaks, and more.

Engine Upgrades

An illustration of engine upgrades that save fuel.
Illustration: The Tom Agency

Cylinder Deactivation

What it is: Shuts off multiple engine cylinders while the vehicle is cruising or coasting.

How it saves fuel: Deactivated cylinders don’t use fuel when the engine is coasting or when the vehicle has a low demand for driving power.

What to watch out for: In some older models, the engine might vibrate when all of the cylinders fire back up.

Which automakers do it well: GM, Honda, Chrysler

Which automakers don’t: None

Smaller Turbocharged Engines

What they are: These engines use forced air to boost their power when needed, giving them horsepower usually found in a larger nonturbo engine.

How they save fuel: Smaller, more efficient engines replace larger ones, using less fuel.

What to watch out for: Many suffer from an initial hesitation due to turbo lag, and sometimes expected fuel-economy savings aren’t realized.

Which automakers do them well: Audi, BMW, Ford (F-150), Honda, Volkswagen

Which automakers don’t: Ford (Focus, Fusion, Escape)

Start/Stop Technology

What it is: Shuts the engine off when the vehicle comes to a stop.

How it saves fuel: By not letting the engine idle when it’s not needed.

What to watch out for: Some systems have a noticeable shudder when they power back on. Some vehicles hesitate when they restart, leaving drivers momentarily flat-footed and unable to merge quickly into traffic. And some systems shut down the air conditioning along with the engine, which can make passengers in the cabin uncomfortable during warm weather.

Which automakers do it well: BMW, Chevrolet (Cruze, Malibu), Honda (Odyssey), Toyota (Sienna), Ford (F-150)

Which automakers don’t: Alfa Romeo, Jaguar/Land Rover, Cadillac

Direct Injection

What it is: Fuel is fed directly into each engine cylinder instead of into an intake manifold.

How it saves fuel: It improves efficiency because the amount of gasoline can be injected more precisely.

What to watch out for: Loud engine clatter can occur in some older vehicles. They’re also prone to carbon buildup, which requires regular maintenance every couple of years to avoid rough idling and a loss of power.

Which automakers do it well: Many; this is a widespread feature.

Which automakers don’t: None; early problems have been largely overcome.

Transmission Advances

An illustration of transmission advances that improve fuel economy.
Illustration: The Tom Agency

8-, 9-, 10-speed Transmissions

What they are: Automatic transmissions with as many as eight, nine, or 10 gears.

How they save fuel: The more gears a transmission has, the more likely that the engine is working at peak efficiency. This means it uses less fuel to generate power.

What to watch out for: Some are poorly tuned and don’t shift smoothly or don’t respond promptly enough, so drivers have to mash the accelerator to get the power they want. This can make a car feel pokey or suffer from jerky gear shifts. And some owners reported reliability issues.

Which automakers do them well: Audi, BMW, Chrysler (8-speed), Genesis (8-speed), Honda (10-speed)

Which automakers don’t: Jeep (9-speed), Honda/Acura (9-speed)

Dual-Clutch Transmissions

What they are: Essentially these have the mechanical guts of a manual transmission, but the gear changes and the clutch operation are executed electronically.

How they save fuel: Fuel economy is improved because less power is lost between the engine and the wheels. Because it doesn’t have a torque converter, there’s a more direct connection between the engine and the wheels.

What to watch out for: They usually hesitate when accelerating from a stop or vibrate in stop-and-go crawl. Many allow the vehicle to roll backward when starting on an incline. Owners have reported reliability problems with some dual-clutch transmissions.

Which automakers do them well: Audi/Volkswagen, Porsche

Which automakers don’t: Ford (Focus and Fiesta), Hyundai (Tucson 1.6T)

Continuously Variable Transmissions

What they are: In essence, CVTs allow for an almost infinite set of gears as opposed to a defined set typically found in an automatic transmission. That allows drivers to get the power they need when they need it, whether it’s passing power instantly or low-effort highway cruising.

How they save fuel: Because they’re always in the right ratio, CVTs optimize fuel economy and acceleration.

What to watch out for: Because the engine may be revving at a higher rate over longer periods than with conventional automatic transmissions, CVTs can amplify engine noise. They can also require more frequent (and sometimes expensive) service compared with conventional automatic transmissions.

Which automakers do them well: Honda, Subaru

Which automakers don’t: Nissan (Versa, Sentra)

Weight Reduction, Tire Tweaks & More

An illustration of weight reduction, tire tweaks, and aerodynamics to improve fuel economy.
Illustration: Tom Agency

Weight Reduction

What it is: Automakers are dropping items such as spare tires and using stronger steel, aluminum, and other high-strength materials to keep weight down.

How it saves fuel: Every pound cut means less weight the engine has to move.

What to watch out for: This can result in less-supportive seats, thinner glass, and fewer sound-deadening materials, which can mean a noisier, less comfortable cabin.

Which automakers do it well: Ford, Honda, Mazda, Mercedes-Benz

Which automakers don’t: Few today; most work hard to avoid making consumers suffer from weight reductions.

Low-Rolling-Resistance Tires

What they are: Tires that create less friction with the road.

How they save fuel: They require less power to roll, reducing work for the engine and helping to save fuel.

What to watch out for: Sometimes the lack of resistance translates into a lack of grip, which can increase wet-stopping distances and lead to a shorter tread life.

Which tire makers do it well: Bridgestone, Firestone, Goodyear, and Michelin market these fuel-saving tires.

Which tire makers don’t: Some car companies and replacement tire makers offer more fuel-efficient tires, but some of those come with compromises to tread life and grip on wet surfaces.

Aerodynamic Improvements

What they are: Automakers are tweaking the slope of hoods, windshields, and rear ends, and adding technology like grill shutters, underbody panels, and wheel covers.

How they save fuel: Sleeker shapes and fewer openings help a vehicle cut through the air more easily.

What to watch out for: Some active systems may require extra maintenance.

Which automakers do this well: All; these efforts have been underway for years.

Editor's Note: This article also appeared in the April 2018 issue of Consumer Reports magazine.