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For oil changes, which matters most: time or mileage?

Most vehicles have recommended maintenance at either time or distance points. As my driving is low mileage, why is it important to follow the time points? Why not just follow the mileage points? – James

As you point out, maintenance schedules are based on time or mileage intervals.

While it may seem to make sense to delay oil changes due to low mileage, the problem is that low mileage. For example, the oil in an engine acts not only as a lubricant, but as a cooling agent and a method of pulling nasty minute and possibly damaging particles caused by wear into the filter and boiling off harmful chemicals caused by combustion.

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Those particles or chemicals might remain in the oil of a lightly used engine. As well, oils and other fluids can break down over a period of time, losing their effectiveness.

One reason for following the recommended intervals is to ensure warranty coverage, the other is to ensure a long and trouble-free life for the engine, transmission, etc.

If the vehicle is off warranty and you don't intend to keep it for years, the monies saved by delaying maintenance may be appealing, but only for the short term.

One important factor to keep in mind when looking at the suggested maintenance schedule is whether your driving pattern falls into the "normal" or "severe" category. You might be surprised to learn that the majority of Canadian drivers fall into the "severe" list, not because we drive like racers but because of our climate and geography.

Severe conditions include frequent trips of less than 15 kilometres, lots of stop-and-go driving, cold weather operation, towing a trailer, dusty roads and idling for long periods. Notice there is no mention of excess speed; the opposite is the case, infrequent use or short hops that never allow the engine and transmission to achieve proper operating temperatures.

I have a couple of vehicles that cover low mileage – 1,000 to 2,000 km a year – one still under warranty and one past that stage. I change the oil annually regardless of mileage or time and ensure that other suggested service items are addressed as well.

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

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