Oil change: how many kilometres, really?
Most modern engines on full synthetic run 8,000 to 12,000 km between changes, and the manual says which. The 5,000 km rule belongs to conventional oil and to engines that are two decades old. The exception matters here: short trips in the cold count as severe service, and severe service means the shorter interval.
Key points
- The manual, not the sticker in the windshield, sets the interval.
- Short winter trips are severe service. Use the short interval.
- The grade on the cap is a specification, not a suggestion.
- Time counts as well as distance: once a year, even on low mileage.
Where the 5,000 km number came from
It was right, for conventional oil in engines designed in the nineties. Oil chemistry has moved a long way since, and a full synthetic in an engine built for it holds its protective additives far longer than the old rule assumed.
Doubling the interval on a modern engine isn't cutting corners, it's what the manufacturer specifies. The number is in the manual, and it's usually between 8,000 and 12,000 km.
Severe service, which is most of us
Every manual carries a second, shorter interval for severe service. Read the definition and it describes an ordinary Repentigny winter: repeated short trips, extended idling, cold starts, stop and go traffic.
The reason is condensation. An engine that never fully reaches temperature doesn't boil off the water and fuel that collect in the oil, and that mixture is what degrades it. A car doing ten minute trips all January is working the oil harder than one doing highway kilometres.
The grade on the cap isn't a suggestion
0W-20 and 5W-30 aren't interchangeable. The first number is how the oil flows cold, and on an engine specified for 0W-20 a thicker oil reaches the top of the engine more slowly on a minus twenty start, which is exactly when wear happens.
Engines with variable valve timing are stricter still: the system uses oil pressure through narrow passages, and the wrong viscosity sets a fault code before it does any damage you can hear.
Time, not just distance
Oil ages in the sump whether the car moves or not. Additives deplete, moisture accumulates, acidity climbs. A car that covers 4,000 km in a year still needs a change once a year.
This is the one most often missed on a second vehicle or a car kept for weekends, where the odometer says everything is fine and the calendar disagrees.
Frequently asked questions
How often should I change my oil?
Follow the manual. On full synthetic it's usually 8,000 to 12,000 km, and the shorter severe service interval if you do a lot of short cold trips, which most drivers here do in winter.
Is synthetic oil worth it?
In our climate, yes. It flows at temperatures where conventional oil is sluggish, which matters most in the first thirty seconds after a cold start, when most engine wear occurs.
What happens if I go too long between oil changes?
The oil loses its additives and starts to varnish, deposits build in the narrow passages, and on engines with variable valve timing that shows up as a rattle at start-up and eventually a fault code.
Do I need an oil change once a year even with low mileage?
Yes. Oil degrades with time as well as distance, and a car doing short trips collects moisture in the sump that never gets boiled off.
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