Once used mostly in trucks, diesel engines are showing up in several new cars and SUVs in Canada, primarily for their power and fuel economy.

“We got rid of all the negatives associated with a diesel, which is the black smoke out the tailpipe, the smell, and the emissions,” says Sylvain Gilbert, manager of technical service, literature and ISO for Mercedes-Benz Canada.

Diesel engines differ from gasoline engines in several ways. They have higher compression, which creates more engine heat. This heat is used to ignite the fuel, unlike a gasoline engine that uses a spark plug.

When the diesel engine is cold, such as if the car has been sitting overnight, a glow plug inside it heats up to initially ignite the fuel. In the past, drivers had to turn the key and wait several seconds for the glow plug to warm up, but in today’s diesels, the plug heats so quickly that diesels take no more time to start than gasoline engines.

Diesels produce more torque than gasoline engines, and do so at lower engine speeds, improving acceleration and towing ability. In many cases, a six-cylinder diesel will produce more torque than an eight-cylinder gasoline engine.

“Traditionally, if you think back 15 or 20 years, diesels were underpowered,” Gilbert says. “Then they started to put turbochargers on them, and perfected the injector system, which improved the power and reduced emissions.”

Because its fuel has a higher energy density than gasoline, and it isn’t revving as high, a diesel engine gets better mileage. The diesel-powered Mercedes-Benz M-Class makes more torque than the six-cylinder gasoline engine, but is rated at a combined 8.9 L/100 km, versus 10.7 L/100 km for gasoline.

Diesel engines are built “beefier” than gas engines because they must withstand the higher compression. This, plus their turbocharger, usually makes them more expensive — the diesel M-Class is $1,500 more than the gas version — but their stronger construction means they traditionally last longer. The company estimates that 80 per cent of M-Class models sold in Canada have a diesel engine. “It’s all about the low-end torque,” Gilbert says.

“People brag about horsepower, but the bottom line is: what pulls you out of the hole and helps you climb that steep hill is torque.”

Check the nozzle colour

At the gas station, the diesel nozzle will be yellow, and sized differently from a gasoline nozzle. If you happen to accidentally put diesel in a gas engine, or gas in a diesel engine, don’t start the vehicle. Have it towed to a shop to get the fuel drained, to prevent engine damage