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The Globe and Mail

Oil change frequency

My owner's manual says I should change my oil every 8,000 kilometres or every three months, whichever comes first. I only drive about 8,000 km per year; do I really need to change my oil four times as frequently as the mileage recommendation? – James

I'd suggest at least once a year, if not twice depending on the type of driving you do.

I have at least two vehicles that accumulate less mileage than that each year and change the oil only once a year.

But I make it a point to avoid short drives, ensuring at least 30 minutes of operation any time they are driven. This allows the oil, coolant and all moving parts to get up to full operating temperature. This ensures condensation and various harmful substances evaporate or go through the various "cleansing" processes and equipment.

If, on the other hand your low mileage includes many short hauls – less than 10 minutes or so – I would suggest changing the oil more frequently.

The issue is that oil acts not only as a lubricant, but as a coolant and flushing agent. As it circulates through the engine adjacent to the combustion chambers, it picks up heat, some of which is lost as the oil goes through the oil pan, which sits down low in the cooling airstream.

More importantly, oil was initially developed to carry small metal particles caused by wear to the filter where they become trapped and removed when the filter is changed. But with the extremely close tolerances of today's engines, there is very little of this metallic wear and oil has become a factor in the search for reducing harmful emissions. Some of the byproducts of the combustion process squeeze past the piston rings and into the oil pan. If the engine and oil are up to temperature, these emissions are dealt with through evaporation. If not, they remain in the oil.

Halifax-based Richard Russell runs a driving school.

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