I have a question about cars with diesel engines. I am fully aware that they are fuel efficient, especially on longer drives, and that modern versions are quiet with good acceleration. But my wife's driving pattern is short drives, usually less than 5 km (shopping, etc.) and of course that happens in the winter too. Does a diesel car achieve good fuel economy and is its performance comparable to a car with a gas engine on a short, cold-weather journey when it probably would not reach optimum engine temperature? – Terry
A diesel engine won't save you money on fuel if you're only taking short trips to the store, and it will end up costing you more than a gasoline engine in the long run.
"I hate to say it, but I don't think diesel's right for this guy," says Volkswagen Canada spokesman Thomas Tetzlaff. "They're quiet, they have great acceleration and extremely good fuel efficiency. But they're really not designed to be driven just five kilometres a day."
Diesel engines don't use spark plugs to ignite the fuel, like gasoline engines do. In a diesel engine, fuel is injected into the cylinders at such high pressure that the air in the cylinders heats up and the fuel ignites. In modern cars, this takes a second or two after turning the key.
Tetzlaff says diesel engines generally need to warm up a bit after starting to get to their ideal operating temperature – when they're most fuel-efficient – especially in the colder months.
"In a span of five kilometres, they're not even going to be remotely warm yet," he says. "A diesel does great in the city. It's not so much the stop-and-go driving that's the problem for this driver. It's just the really short distances each day.
"If it were a bunch of five kilometre trips in one day, that would be okay," Tetzlaff says.
Diesel engines can be incredibly fuel efficient when the engine is running for longer periods and is kept at a consistent temperature – they need to be hot.
"We've had customers go 1,500 km (on one tank) with a Passat diesel on one trip," Tetzlaff says. "But that's doesn't mean you can go 300 days without filling up if you're just going to the store and back."
Short running times are bad for a diesel engine, and will hurt it's efficiency and reliability, says Patrick Brown-Harrison, an automotive instructor at SAIT Polytechnic in Calgary. And, because the engine has to warm the coolant before any heat makes it into the passenger compartment, diesels have traditionally taken longer to get comfortably warm inside in the winter.
"Some manufacturers install pre-heaters or you can put in an aftermarket one to make sure that your passenger compartment gets warm a little faster," Brown-Harrison says.
Both Tetzlaff and Brown-Harrison suggest gasoline, a hybrid or even electric vehicles for a car that will just be used for quick jaunts across town.
"If you're driving 10,000 km a year (about 25 km or less a day), you should be driving a gasoline-powered car or looking at a hybrid," Tetzlaff says. "Between 10,000 and 20,000 km a year, gasoline is great. But if you're driving more than 20,000 km a year, well, you're a prime candidate for diesel."
Diesels are ideal for drivers who rack up a lot of mileage, he says – they're fuel efficient and their drivability is as good if not better than a vehicle with a gasoline engine.
"But somebody who isn't driving much won't see the savings that a high mileage customer will," Tetzlaff said. "And ultimately, it will cost them more out of pocket. Our diesel engines cost more than gas, around a $2,000 premium."
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