Synthetic vs. conventional oil: what your engine actually needs

Oil is the cheapest insurance in your engine. Picking the right one is simpler than the marketing makes it sound.

What the manual says wins

Every engine has a specified oil weight (e.g. 0W-20) and an approval standard (e.g. API SP, dexos1 Gen 3). Use what the manual lists. Anything else risks warranty and longevity.

Full synthetic is now standard

Most cars built after 2012 require full synthetic. It flows better cold, holds viscosity hot, and resists breakdown over longer service intervals. The price gap to conventional is small — often $20–$30 per change.

When conventional still makes sense

Older engines (pre-2000s) with high mileage sometimes do better on conventional or a high-mileage blend. The thicker base oils and seal conditioners can quiet leaks and reduce consumption.

Change interval reality

"15,000-mile" intervals are theoretical. In LA stop-and-go, 5,000–7,500 miles is a more honest number for full synthetic. Short trips and idle time age oil faster than freeway miles.