Car care · Elgin Auto Sales & Service Center · Elgin, IL
How Efficient Is a Gas Engine?
Most of the gasoline you buy never actually moves your car down the road. Here is where the energy goes, according to fueleconomy.gov, the U.S. government fuel economy site, and how diesel and electric vehicles compare.
12% to 30%of fuel energy moves a gas vehicle down the road
Heatwhere most of the lost energy goes
One-thirdmore efficient, generally: diesel vs. gasoline engines
Over 77%of grid energy reaches the wheels of an EV
The short answer
Not very. Fueleconomy.gov says only about 12% to 30% of the energy from the fuel you put in a conventional vehicle is used to move it down the road, depending on the drive cycle. Most of the rest is lost in the engine, primarily as heat, with smaller losses in the transmission and driveline and some energy used to power accessories.
Where the energy in gasoline goes
Fueleconomy.gov breaks down where a gasoline vehicle's fuel energy is lost:
| Loss | What happens |
|---|---|
| Engine losses | Most of the fuel's energy is lost in the engine, primarily as heat; smaller amounts go to engine friction, pumping air in and out, and combustion inefficiency |
| Driveline losses | Energy is lost in the transmission and other parts of the driveline |
| Accessories | Seat and steering wheel warmers, lights, wipers, navigation and entertainment systems use energy; the water, fuel and oil pumps, ignition and engine controls also run off the engine |
| Braking | Energy used to get the vehicle moving is lost as heat through friction at the brakes |
| Idling | In stop-and-go city driving, a vehicle spends significant time idling, using energy to run the engine and accessories; highway driving includes little to no idling |
From Where the Energy Goes: Gasoline Vehicles (fueleconomy.gov), read November 9, 2026. Energy use and losses vary from vehicle to vehicle.
What reaches the wheels then has to overcome wind resistance (aerodynamic drag), which grows as speed increases, and rolling resistance from the tires. Fueleconomy.gov says new tire designs and materials can reduce rolling resistance; for cars, a 5% to 7% reduction increases fuel efficiency by 1%. For tire care basics, see how to check tire pressure.
Gas vs. diesel vs. electric efficiency
Here is how fueleconomy.gov compares the three:
| Vehicle | Efficiency, per fueleconomy.gov |
|---|---|
| Gasoline vehicle | About 12% to 30% of fuel energy moves the vehicle down the road |
| Diesel engine | Inherently lower losses; generally one-third more efficient than gasoline engines |
| All-electric vehicle | Converts over 77% of the electrical energy from the grid to power at the wheels; the electric drive system loses only 15% to 20%, compared with 64% to 75% for a gasoline engine |
From Where the Energy Goes: Gasoline Vehicles (fueleconomy.gov), All-Electric Vehicles (fueleconomy.gov) and Where the Energy Goes: Electric Cars (fueleconomy.gov), read November 9, 2026.
Electric vehicles also use regenerative braking to recapture braking energy and waste no energy idling; see auto start-stop explained for how start-stop systems cut idling.
Technologies that make gas engines more efficient
Fueleconomy.gov says advanced technologies can reduce engine losses. It lists these, with their potential efficiency improvements:
| Technology | What it does | Potential efficiency improvement |
|---|---|---|
| Turbocharging with engine downsizing | A compressor forces more air (and fuel) into the cylinders, so a smaller engine can make the power of a bigger one | Up to 8% |
| Cylinder deactivation | Turns off some cylinders when they are not needed | Up to 5% |
| Variable valve timing and lift | Adjusts when, how long and how far the valves open to suit engine speed | 3% to 4% |
| Gasoline direct injection | Injects fuel directly into the cylinder, allowing higher compression or better spark timing | 1% |
From Advanced Engine Technologies (fueleconomy.gov) and Where the Energy Goes: Gasoline Vehicles (fueleconomy.gov), read November 9, 2026. Estimates come from a 2015 National Academy of Sciences study, most values rounded down; real-world results vary by vehicle.
Fueleconomy.gov adds that transmission designs such as continuously variable transmissions (CVTs) can reduce driveline losses; see what is a CVT transmission.
Service at Elgin Auto Sales & Service Center
Regular maintenance helps keep your engine running as intended. Schedule service or see our service specials.
Our service department at 1200 E. Chicago St. in Elgin is open Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m., and is closed Sunday. Get directions.
Engine efficiency FAQ
How efficient is a gasoline engine?
Fueleconomy.gov says only about 12% to 30% of the energy from the fuel in a conventional vehicle is used to move it down the road, depending on the drive cycle.
Where does the wasted energy go?
Mostly to heat in the engine; smaller amounts go to engine friction, pumping air and combustion inefficiency. Energy is also lost in the transmission and driveline, used by accessories, and lost in braking and idling, per fueleconomy.gov.
Are diesel engines more efficient than gas engines?
Yes. Fueleconomy.gov says diesel engines have inherently lower losses and are generally one-third more efficient than their gasoline counterparts.
Are electric cars more efficient than gas cars?
Yes. Fueleconomy.gov says EVs convert over 77% of the electrical energy from the grid to power at the wheels, compared with about 12% to 30% of fuel energy for gasoline vehicles.
Do tires affect efficiency?
Rolling resistance from the tires uses energy. Fueleconomy.gov says new tire designs and materials can reduce it; for cars, a 5% to 7% reduction in rolling resistance increases fuel efficiency by 1%.
What are your service hours?
Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m. We are closed Sunday.
Shopping for a used car?
Visit us at 1200 E. Chicago St. in Elgin.
Sources
Energy loss and efficiency information is from fueleconomy.gov, the U.S. government fuel economy site administered for the Department of Energy and the EPA, read November 9, 2026. This is general information; your owner's manual is the authority for your vehicle. Our address and service hours are from our own website, checked the same day. Photo is of our dealership.
- Where the Energy Goes: Gasoline Vehicles (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Where the Energy Goes: Electric Cars (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- All-Electric Vehicles (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Advanced Engine Technologies (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Service page: address and hours, Elgin Auto Sales & Service Center, read November 9, 2026