How often should you change your car's engine oil: kilometres or months?

The short answer

There is no single number. Your owner's manual gives a distance and a time, and you change the oil when the first of the two is reached. The manuals read for this guide ranged from 15,000 km or 12 months to 20,000 km or 24 months for normal use, and halved or worse for severe use. Use the figure for your exact engine, market and model year.

What the manuals say

These are examples, not a table to copy. Each applies only to the engine and market named.

• Hyundai, Europe (Smartstream engines, 2025 manual): diesel D1.6, replace every 20,000 km or 24 months; petrol G1.6 T-GDi, G2.0 and G2.5 GDi, every 15,000 km or 12 months. The page also says to change when the instrument cluster shows the oil-exchange message.
• Kia, Australia and New Zealand (1.4 MPI petrol, non-turbo): every 15,000 km or 12 months.
• Mazda 3, Canada: every 16,000 km (10,000 miles) or 12 months, or when the maintenance light or display alerts you, whichever comes first.

Same idea, different numbers. That is why a rule like "every 10,000 km" from a friend or a garage poster may be wrong for your car, in either direction.

What counts as severe use

Manuals shorten the interval for harder use, and the definitions differ.

• Hyundai Europe lists conditions such as repeated trips under 8 km in normal temperatures (16 km in freezing weather), long idling or low-speed driving, dusty or salted roads, heavy traffic, repeated mountain driving, towing or roof loads, and using a non-recommended oil. For those, the diesel 1.6 moves to 10,000 km or 12 months and the petrol engines above to 7,500 km or 6 months.
• Mazda Canada says to change at 8,000 km (5,000 miles) or 6 months if you regularly idle for long periods, drive in dust, make long trips in the cold or only short trips, drive in extreme heat, or drive continuously in mountains.

If most of your driving is short city trips, check whether your manual's severe schedule describes you.

Does skipping the dealer void the warranty?

The EU competition rules address this directly, with a limit worth knowing. The Commission's supplementary guidelines on motor vehicles say that making a manufacturer's warranty, legal or extended, conditional on having repair and maintenance work done only inside the authorised network can raise competition-law concerns. The same applies to requiring the manufacturer's own brand of spare parts for replacements not covered by the warranty. But the guidelines also say a manufacturer may legitimately refuse a claim that is causally linked to a repair or maintenance operation done incorrectly, or to poor-quality parts.

Two cautions. These are competition-law guidelines about the manufacturer's agreements, not a consumer rights manual, and your warranty document may add its own conditions. Block exemption Regulation (EU) No 461/2010 was extended by Regulation (EU) 2023/822 to 31 May 2028. I did not read the Greek or other national law on this. In practice: follow the manual's intervals, use oil that meets the specification it names, and keep dated invoices showing what was done.

Before you rely on this

Only three manufacturers' manuals were read, none for every market, and Toyota, Volkswagen, Ford, Renault and others were not checked. The Hyundai pages are for Europe; the Kia and Mazda pages are for other markets. The owner's manual or service booklet for your car is the authority, and the warranty's own text decides what it requires.

Track it in Epimeleia

Add your car as an item, note the manual's distance and time interval, and set a reminder for whichever comes first. Log the date and odometer reading at each change, with the invoice attached, so the history is there if a warranty claim ever questions it.