Why are diesel engines more efficient?

Why are diesel engines more efficient than gas engines?

Scott J, Chicago

We get this question a lot, as people often associate diesel engines with semi-trucks and large pickups that don’t seem to represent fuel efficiency. Yet diesel passenger cars on the market now, like the Volkswagen Jetta TDI and Mercedes-Benz E-320 CDI, do have gas mileage ratings on par with much smaller compact cars that use less-powerful gasoline engines.

According to an Automotive Service Excellence representative, diesel engines — whether in a semi or a Jetta — are more efficient because of the diesel engine process, which burns fuel at a much higher temperature than regular gasoline engines, promoting more-efficient fuel combustion.

Also, diesel fuel has a higher energy density than standard gasoline, meaning it takes less fuel to provide the same power as standard gasoline.

There are a couple of reasons why diesel engines in passenger cars haven’t gained popularity in the U.S., even though they are efficient. Besides the fact that not every gas station has a diesel pump, there are also the stigmas of soot-puking tailpipes, oily fuel residue and noisy engine clanking associated with previous generations of diesel cars. Today’s modern diesel passenger cars are surprisingly quiet, as well as clean burning, and produce little or no tailpipe soot due to advancements in engine technology and the new clean-diesel fuel that is now the only diesel fuel sold in the U.S.

Learn more

Answered by Joe Bruzek on May 4, 2007 in How Does That Work? | Permalink

Search Results

Ask.cars.com Search Results for


See if your question has already been asked and answered

Thank You!

Your question has been successfully submitted to Ask.cars.com. It will now be reviewed by our editors and we'll answer it soon if we think it's a useful question. You will be notified via e-mail when the answer is posted. Ask.cars.com tackles your questions about new cars and the car-buying process. Unfortunately we can't answer questions regarding:

  • Used cars.
  • Most aftermarket products.
  • Mechanical issues. You can visit our friends at Car Talk to discuss your mechanical problems.
Thanks for your interest.


Have our experts answer any of your questions about new cars.

Email us at tips@cars.com

Maintenance Advice
Get answers from the
Car Talk Community