OIL CHANGE INTERVAL

The intervals by oil type

The general answer is every 5,000–7,500 miles. Underneath it the oil type does most of the work: 3,000–5,000 miles on conventional, and 7,500–10,000 miles on a full synthetic.

Those are generic figures. Manufacturers publish an interval for each engine and many modern ones specify 10,000 miles or a computed interval — that published number is the one that governs, particularly while the car is under warranty.

Why the 3,000-mile rule persists

It was correct in the era of non-detergent oils and much less precise engines. It survives because it is memorable, because a sticker in the windscreen is a marketing instrument, and because nobody has ever been sued for changing oil too often.

On a modern engine running synthetic, changing at 3,000 miles is not harmful — it is simply paying two to three times for the same protection. That is a real cost against a band of $35–$75 per service, several times a year.

What severe duty actually means

Manufacturers publish a second, shorter schedule for severe service, and the definition is broader than most drivers assume: repeated short trips that never bring the oil to operating temperature, extended idling and stop-and-go traffic, towing or carrying heavy loads, dusty conditions, and sustained extreme heat or cold.

Time, not only miles

Oil ages whether or not the engine turns. Additives deplete, moisture accumulates, and acids form. A car driven 3,000 miles a year still needs its oil changed on the owner's-manual schedule, not on miles alone.

The same logic applies across the maintenance schedule — tyres rotate every 5,000–8,000 miles or every six months, or every 5,000 miles or less on all-wheel drive, and brake fluid absorbs moisture on a calendar rather than an odometer, which is the whole argument of the brake fluid guide. Rotation is often confused with an alignment; the difference is laid out in tire rotation vs wheel alignment.

Oil life monitors

Most cars built in the last fifteen years compute an oil life percentage from engine revolutions, temperature history, trip length and idle time. It is a genuinely better instrument than a mileage sticker, because it observes how the car is actually driven rather than assuming.

Put the resulting interval on a service card and hand it over. Trust the monitor, and reset it after every change — a monitor never reset gives a number that bears no relation to the oil in the sump. If you want to know what the service will cost before you book it, that is the oil change price guide.