Synthetic vs Conventional Oil
Reviewed by GarageDex editorial
Full synthetic oil is engineered for more uniform molecules, so it flows better when cold, holds up better under heat, and lasts about twice as long between changes - at a higher price. Conventional (mineral) oil is cheaper and fine for older, low-stress engines. The deciding factor is simple: use what your owner's manual specifies. Most engines built in the last decade require full synthetic.
Quick comparison at a glance:
| Full synthetic | Conventional | |
|---|---|---|
| Drain interval | 7,500-10,000 mi | 3,000-5,000 mi |
| Cold-start flow | Excellent | Fair |
| High-heat protection | Excellent | Good |
| Cost per change | Higher | Lower |
| Best for | Modern & turbo engines | Older low-mileage engines |
Why synthetic became the default
Modern engines run hotter, with tighter tolerances, turbochargers, and longer service intervals. Conventional oil breaks down and forms sludge faster under those conditions, which is why most manufacturers now specify full synthetic and why putting conventional in an engine that calls for synthetic can shorten its life.
When conventional still makes sense
Older, naturally aspirated engines that were designed for conventional oil and get driven gently are fine on it, especially if they are changed on time. If you are unsure, synthetic is never the wrong choice - the reverse is not always true.
Viscosity matters more than the type
Whichever you choose, use the right grade (like 0W-20 or 5W-30). See the exact oil type and capacity for your car and our viscosity comparisons.
Frequently asked
Can I switch from conventional to synthetic oil?
Yes. Switching to synthetic is safe in any engine and is an upgrade - it does not harm seals or cause leaks in a healthy engine, despite the old myth. Just use the viscosity your manual specifies.
Is synthetic oil worth the extra cost?
Usually yes. It lasts roughly twice as long, so the per-mile cost is similar, and it protects better in heat, cold, and stop-and-go. For modern or turbocharged engines it is required, not optional.
What is synthetic blend oil?
A mix of synthetic and conventional base oils. It costs less than full synthetic and performs better than conventional - a middle option, though many newer engines still require full synthetic.
Need your car's exact spec? Find your car's oil type & capacity →