The synthetic-versus-conventional question comes down to three things: your engine's age, how you drive, and what your manufacturer actually recommends. Here's how to sort it out without the upsell.

Conventional oil

Refined directly from crude oil with minimal processing, conventional oil is the most affordable option and works fine for older, lower-mileage engines with simple designs. If your car is older, has fewer than the "severe driving" conditions described by your manufacturer, and you change oil on a shorter interval, conventional oil is a reasonable, budget-friendly choice.

Full synthetic oil

Synthetic oil is chemically engineered for more consistent molecule size, which means better performance across a wider temperature range, slower breakdown over time, and better protection during cold starts — a real advantage on damp Seattle mornings. It typically costs more per change but lasts longer between changes, which narrows the price gap over a year of driving.

Synthetic blend

A middle ground: part synthetic, part conventional. It offers some of synthetic's benefits at a lower price point than full synthetic, and can be a reasonable choice if your manufacturer doesn't specifically require full synthetic.

How to actually decide

  • Check your owner's manual first. Many newer vehicles, especially turbocharged engines, require full synthetic — using conventional oil can void warranty coverage.
  • Consider your commute. Frequent short trips and stop-and-go traffic favor synthetic, which handles heat cycling better.
  • Factor in total annual cost, not just price per change. Synthetic costs more upfront but needs changing less often.
  • High-mileage engines (past 75,000 miles) may benefit from high-mileage formulations, available in both conventional and synthetic, designed to condition aging seals.
One thing to watch for: ask specifically what grade and brand of oil a shop uses. "Synthetic" isn't a single standardized product, and quality varies between suppliers.

Whichever you choose, consistency matters more than the specific choice — sticking to a proper interval with a quality product will do more for your engine's lifespan than agonizing over the synthetic-versus-conventional decision alone.