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I'm about to buy a new car and am thinking of going for a diesel engine. I've heard they are cheaper and better for the environment but is this really a good choice? – Emma in Edmonton

A good choice for you really depends on your values, budget, and driving habits. With diesel fuel now equal, if not more expensive, than gasoline and a higher purchase cost for a diesel-powered vehicle, what are the advantages?

Fuel economy is certainly much better with a diesel engine, which is the prime reason for their popularity in Europe. A diesel engine will also last much longer than its gasoline counterpart.

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"You can get up to maybe 250,000 km or 300,000 km before a gas engine starts to make noise, or burn oil because it's wearing out, but a diesel can quite easily do 500,000 km and still be in excellent shape," says one certified mechanic I spoke with.

"That's because diesel is a very light oil, and when you burn diesel in an internal combustion engine you're basically lubricating the valves, rings, and piston walls. Gasoline and diesel both derive from petroleum, but gasoline on the other hand is very detergent, so it continually washes away any oil from the engine components."

Properly maintained, most mechanics agree you can expect to keep a diesel vehicle on the road for a solid 30 years. They do, however, require some special care. For example, you can't expect a diesel to sit all day in sub-zero temperatures and start easily. In an Edmonton winter, you'll likely need starting fluid to get the engine running.

Diesel engines generally last longer, but they can be costly to repair. For starters, diesels have an intricate and expensive fuel pump. In addition, any water inadvertently passing through a diesel's injectors or distribution pump will cause major damage, so the engine oil filters are also unique. These extra filters must be changed regularly, and they're not cheap. For example, a special water separator filter, which keeps moisture out of the fuel, can cost up to $100.

Fuel availability is also a consideration as not all service stations offer diesel, so you'll need to make sure you have a reasonably convenient supply.

Let's move on to the environmental impact. Which vehicle type is better? According to Dr. David R. Boyd, adjunct professor of resource and environmental management at Simon Fraser University, that depends.

"Regarding used vehicles, diesels are more efficient (thus releasing fewer greenhouse gas emissions), but dirtier (releasing more conventional air pollutants, including particulate matter)," says Dr. Boyd.

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"As for new vehicles, I would rank hybrids first. There's a reason taxi fleets have adopted them en masse.

"Hybrids outperform other vehicles in fuel efficiency and reduced emission of air pollutants. New diesels in conjunction with new regulations requiring ultra low sulphur diesel fuel are much cleaner than diesels of the past. However, concerns regarding emissions of particulate matter, nitrogen dioxide, and air toxics remain," says Dr. Boyd, whose latest book is Dodging the Toxic Bullet: How to Protect Yourself from Everyday Environmental Health Hazards.

The diesel engine is undoubtedly more efficient than gas, so if you're doing lots of kilometres, your fuel costs will be lower. There are better choices for the environment though these days in terms of fuel economy and emissions, and so if you do have the extra cash to spend upfront, why not try a hybrid?

E-Mail Ask Joanne at globedrive@globeandmail.com

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