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How often should I change the oil in my car?

I am confused about routine oil change intervals for my 2012 Ford Focus. The driver's manual says to change oil every 15,000 kilometres or when the service light comes on, as the car has an intelligent oil life monitoring system. The Ford service adviser insists on changing oil every 8,000 kilometres. Who should I believe? – Shabbir in Mississauga, Ont.

Believe the manufacturer and the service light. Increasing the frequency of oil changes is common practice among dealerships as a way to generate traffic and business for the service department.

One downside to making motor vehicles more reliable and efficient is that they require less service, less often. That means less business for new car dealer service departments.

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There may be occasions, under a certain type of driving conditions, when more frequent changes are recommended, but that is the role of the oil monitoring system to determine that interval. As long as your driving style or habits fit those explained in the manual under regular or severe use, you are fine with the system adviser, not the one at the dealer.

It is the manufacturer, not the dealer who warrants the engine and has to pay for problems that occur during the warranted life of the engine and it is the manufacturer who thus knows best what is required to maintain that engine.

When the engine was under development, the manufacturer ran it under millions of miles of tests to not only determine what type of oil to use, but how long it can be expected to last before breaking down and losing some of its properties under a wide variety of conditions. This information is used to establish the oil change intervals recommended in the manual.

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

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