Diesel Engines Versus Gas Engines

view of Honda engine

NRMA Motoring and Services/Flickr/CC BY 2.0


What's the difference between a diesel engine and a gas engine? Is one better than the other? Depending on what you need it for, and your personal preferences, in some instances a diesel engine may be a better option than gas. For instance, fuel economy is a big consideration for many people when considering which vehicle is a good fit for them.

To make that decision, it's useful to understand the differences between the two types of engines.

Gas Versus Diesel Engines

In a modern gasoline engine gas, or fuel, is delivered to each cylinder of the engine by a fuel injector. The injector sprays a fine mist of fuel into each cylinder just above the intake valve. This mixes with air that comes in through the air filter and related air intakes, then flows through the intake valve of each cylinder.

In a diesel engine, the fuel is injected directly into the cylinder. mixing with the air there. The diesel injector is within the combustion area of the engine, so diesel fuel needs to be "tougher" than gasoline. 

Fuel Economy and Diesel Engines

Diesel engines get better fuel economy simply because they do not need to burn as much fuel as a gas engine to get the same power. Diesel engines are also built heavier than a gas engine to sustain the added stress of the higher compression ratio. Diesel engines do not have an ignition system so you will never have to give them tune-ups. Exhaust systems last longer because diesel fuel exhaust is not as corrosive a gasoline engine exhaust.

Diesel Engines and Noise

One big downside of diesel engines: They are very noisy. You will get the typical diesel clatter at idle, but that goes away off idle. At normal driving speeds, they are as quiet as a gasoline engine. You won't get the same acceleration that you get from a gasoline engine, but a turbo diesel will get up and go fairly quickly. You will need to adjust your driving habits somewhat also.

Maintenance of Diesel Engines

With gas engines but especially with diesel engines, regular oil changes are a must. Diesel fuel is not as refined as gasoline and the oil will get dirtier than a gasoline engine. Replace air and fuel filters once a year. If you live in a cold climate, you will need to switch to a winter blend fuel to prevent fuel gelling. There are additives you can put in the fuel to help prevent this as well.

Keeping Diesel Engines Warm

Replace glow plugs (the heating devices used to warm diesel engines so they start) every two years as well. If temperatures drop below 10 degrees Fahrenheit, it's probably not a bad idea to use a block heater. This will ensure that your diesel engine starts easily in cold weather, especially with the heavier grade oil that diesel engines require. Just be sure you know what you're doing; ask a mechanic for assistance if you want to install a block heater.