Synthetic vs Conventional Oil
Written by Muneeb Rana · Last updated 21 October 2026
Quick answer: In the synthetic vs conventional oil debate, synthetic usually wins on protection: it resists breakdown at high temperatures, flows better in the cold and often allows longer change intervals. AAA's testing found synthetic outperformed conventional oil on average. It costs more per change. Use whatever grade and specification your owner's manual requires.
TL;DR
- Synthetic protects better and lasts longer; costs more.
- Many newer engines require synthetic.
- You can switch between them; follow the manual's grade.
Synthetic vs conventional oil comes down to protection, interval and price. Here's how they compare, what blends and high-mileage oils are, and how to choose.
Comparison table
| Full synthetic | Synthetic blend | Conventional | |
|---|---|---|---|
| Heat and cold performance | Best | Good | Basic |
| Typical interval | 7,500-10,000+ mi | 5,000-7,500 mi | 3,000-5,000 mi |
| Cost per change | Highest | Middle | Lowest |
| Required by | Many newer, turbo and high-performance engines | Some | Older engines |
Intervals are typical; your manual decides. Use the oil change interval calculator.
What AAA found
AAA's independent testing reported that synthetic oils performed on average 47% better than conventional oils across its industry-standard tests, and recommended synthetic for vehicles that would benefit, such as those that tow or make frequent short trips. Read AAA's summary.
Can you switch or mix?
Yes, you can switch between conventional and synthetic, and they're compatible if mixed, as long as the oil meets your manual's viscosity grade (for example 0W-20) and specification. FuelEconomy.gov notes using the manufacturer's recommended grade can improve fuel economy by 1-2%.
High-mileage oil
High-mileage oils contain seal conditioners meant to reduce leaks in older engines. They can help some engines past about 75,000 miles but aren't a fix for a real leak. See high-mileage car maintenance.
Log your oil type
Record the oil grade and brand with each change so the next shop uses the same. CarO's car repair log keeps it with the receipt; see how often to change oil and how to check oil level.
Download CarO free on the App Store or Google Play. Free with ads; optional in-app purchases.
Sources
- AAA: Synthetic vs. Conventional Oil: www.aaa.com (accessed 21 October 2026)
- AAA: How Often Should You Change Your Oil?: www.aaa.com (accessed 21 October 2026)
- FuelEconomy.gov: Keeping Your Vehicle in Shape: www.fueleconomy.gov (accessed 21 October 2026)
- Consumer Reports: Essential Oil Change Rules Every Car Owner Needs to Know: www.consumerreports.org (accessed 21 October 2026)
Disclaimer: CarO and this website give general car-care information, not professional advice. Maintenance intervals and specifications vary by vehicle, so always follow your owner's manual and a qualified mechanic. Mileage and cost figures are estimates; check local tax rules before using any log for deductions.
FAQ
Is synthetic oil better than conventional?
For protection and longevity, generally yes. AAA's testing found synthetic performed better on average. It costs more, so the value depends on your engine and driving.
Can I switch from conventional to synthetic oil?
Yes, at any oil change, as long as the oil meets the grade and specification in your manual.
Is it bad to mix synthetic and conventional oil?
No, they're compatible. A mix just won't give the full benefits of synthetic.
How long does synthetic oil last?
Often 7,500-10,000 miles or a year, but follow your manual or oil-life monitor.
Do older cars need synthetic oil?
Not usually unless the manual says so, but many older engines can use it. Follow the manual's grade.
Related guides
Track this in CarO
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