Skip the auto shop - Our mechanics make house calls

What Is the Difference Between a Diesel and a Gasoline Engine?

diesel v gasoline

Although new power sources like natural gas, hybrid-electric vehicles, and E-85 are increasing in popularity, most combustion engines sold in the United States are still powered by unleaded gasoline or diesel fuel. Although the chemical differences between these two fuels is significant, how engines use these fuels to create power is quite similar. Let's break down the differences and similarities in the fuels and engines so you can make an informed decision on which to choose.

What’s the difference between gasoline and diesel fuel?

Essentially, gasoline and diesel fuel both come from petroleum, but have different methods of refinement for use. Unleaded gasoline is more refined in general than diesel. It is comprised of multiple carbon molecules that range in size from C-1 to C-13. During combustion, gasoline is combined with air to create a vapor, then ignited to produce power. During this process, larger carbon molecules (C-11 through C-13) are much harder to burn, which is why it’s estimated that only 80% of fuel burns in the combustion chamber during the first attempt.

Diesel fuel is less refined and ranges from C-1 carbon molecules to C-25 in size. Due to the chemical complexity of diesel fuel, the engines require more compression, spark and heat to burn the larger molecules in the combustion chamber. The unburned diesel fuel eventually is pushed out of cylinder as ‘black smoke’. You may have seen big trucks and other diesel vehicles spewing black smoke out of the exhaust, but diesel technology has improved to the point of being an eco-friendly option with very little emissions.

Gasoline and Diesel Engines are More Alike Than Different

In truth, a gasoline and diesel engine are more alike than different. Both are internal combustion engines, which convert fuel into energy through controlled combustion. Fuel and air are mixed and compressed in both types of engines. The fuel must ignite to provide the power needed for the engine. They both utilize emission control systems, including an EGR recirculation system to attempt to re-burn particulate matter in the combustion chamber. They also both use fuel injection as their primary sources of induction. Many diesels utilize turbochargers to force more fuel volume into the combustion chamber to expedite the burning of fuel.

How They are Different

The difference between diesel and gas engines is how they ignite the fuel. In a gasoline engine, the fuel and air are compressed together in a specific point in the cycle just before the piston is pushed up to reach the spark plug. The spark plug ignites the mixture, driving the piston down and sending power through the drivetrain to the wheels.

In a diesel engine, the fuel and air mixture is compressed early in the combustion process, which produces enough heat to generate to combust and ignite the fuel. No spark plugs are necessary for this process. The term used for this is compression ignition. When a similar effect happens in a gas engine, you hear a knocking sound, which indicates possible damage to the engine. Diesel engines are built to perform this way in normal operation.

Horsepower and torque is another area where these two engines differ, and it may be the most important for your purposes. Diesel engines produce a higher level of torque, which is what gets the vehicle moving, especially with heavy loads, so they're ideal for towing and hauling heavy loads. Gasoline engines generate more horsepower, which spins the engine faster, allowing for better acceleration and top speed.

Usually, a manufacturer will offer the same vehicle with either a gasoline and diesel engine. The different engines will drive very differently and vary in performance based on exact specifications, so it’s best to compare the details and go for a test drive when you’re deciding which vehicle to buy.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....
Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed Related Trouble Codes: P2441: EVAP Vent Valve Stuck Open EVAP trouble...


Related questions

Q: The vehicle rides rough and there is a loss of power

Your vehicle has only 69,000 miles and so you want to make sure that the ball joint(s) has actually failed. So, best to either get a second opinion and have the Mechanic demonstrate the failure to you so you can...

Q: Fuel line has water

If the fuel is contaminated with water, the entire fuel system will need flushed to avoid damage to the injectors. I suggest having a qualified technician, such as one from YourMechanic, come to you home or office to drain your...

Q: Loss of power at 40 to 50 mph.

Check the throttle pedal position sensor on the gas pedal and see if the wiring is loose or pinched. If the wiring looks good and is not damaged, then I recommend replacing the sensor. If you need further assistance with...