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My buddy heard from a mechanic that owner's manuals recommend oil changes more frequently than cars actually need. Is it all a big cash grab?

– Dave, Montreal

I've been looking for that mechanic ever since I started writing this column. But so far, every car expert I've interviewed say manufacturer's maintenance schedules are fair.

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"To people who say maintenance schedules are just there to make dealer's money, I would ask 'Do you go to your dentist for the recommended checkups or to your family doctor for your annual physical?'" said Stephen Leroux, automotive professor at Centennial College. "The point is, your vehicle needs to stay healthy too – isn't it worth a few dollars to make sure that vehicle is going to operate efficiently and safely?"

Leroux said maintenance schedules are usually designed for average driving: 15,000 to 20,000 km a year.

If you put extra strain on your vehicle – say, from pulling a trailer, constant stop-and-go-driving or extremely low annual mileage – you'll need to get oil changed more often than recommended.

"An example of this would be a vehicle that has a suggested oil change interval of 12,000 km yet the owner only drives the vehicle 2,000 km a year," Leroux said. "It would be in the customer's best interest to change the oil yearly to prevent sludge build up and or condensation build up in the oil system."

This is why most manuals specify a set time period or mileage. It's always whichever one comes first.

Even if you haven't driven much, over time condensation in oil becomes corrosive to your engine and sludge plugs oil galleries, Leroux said.

Of course, you've got to follow the schedule – or the oil life monitoring system if your vehicle has one – or you'll void the warranty.

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But, even then, the manufacturers' recommendations are in line with what your vehicle needs, said BCIT head instructor Mubasher Faruki, when I asked him this question during an interview about storing a car for the winter.

"The best advice is to check the manual and see what service the manufacturer recommends," he said. "They're not making this stuff up."

Consumer Reports magazine says to stick to the service intervals in your car's service manual. Most vehicles are designed to go at least 12,000 km between oil changes.

The magazine did report that quick-lube places will recommend oil changes every 5,000 km – and that's usually more often than most vehicles need. Changing oil more often won't hurt, but it'll cost more money.

Leroux's message to drivers griping about maintenance schedules?

"Today's vehicles are expensive sophisticated pieces of equipment and many transport priceless cargo in the form of children and loved ones," he said. "Isn't it worth a few dollars to make sure that vehicle is going to operate efficiently and safely?"

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What do you think? Join the conversation below.

Send your automotive maintenance and repair questions to globedrive@globeandmail.com

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