You’ve got your eye on a stylish but rugged new truck and you’ve discovered you have the option of either a diesel or gasoline engine. If you don’t understand the difference, you may not know which one to choose.

More alike than different

In truth, a gasoline and diesel engine are more alike than different. Both of them are internal combustion engines, which convert energy into fuel through small combustions or explosions. Fuel and air are mixed and compressed in both types of engines. The fuel must ignite to provide the power needed for the engine.

How they are different

The difference between diesel and gas engines is how the components 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 turning the crankshaft to power the transmission and turn the wheels.

In a diesel engine, the fuel and air mixture are compressed together early in the combustion process, which causes enough heat to generate to combust and ignite the fuel. No spark plugs are necessary for this process. The term used for what happens 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.

Another difference is in the type of fuel used in the two engines. Diesel fuel is more like watered-down gasoline. Less diesel fuel is required for the same amount of energy than gasoline even though it is often more costly in price.

Horsepower and torque is another area where these two engines differ, and it may be the most important for your purposes. Diesel engines have a higher level of torque, which is what gets the vehicle moving, especially with heavy loads. Gasoline engines are better at horsepower, which rev up higher.

Both types of engines vary in performance based on the manufacturer and exact specifications, so it’s best to compare specs on the engine when you’re deciding which vehicle to buy.

This article originally appeared on as What Is the Difference Between a Diesel and a Gasoline Engine? and was authored by Joyce Morse.

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