Oil Comparison · Reviewed Oct 3, 2026
AMSOIL Synthetic over Conventional Oil: Which Is Better? (2026)
Synthetic oil usually protects better and lasts longer, and conventional costs less up front. Here is what independent testing shows and how to choose for your engine.
By Alan Williams, independent AMSOIL Dealer since 2004, Tomball, TX
Is synthetic oil better than conventional?
In AAA testing of 5W-20 oils, synthetic oils performed an average of 47% better than conventional across eight industry-standard tests. AAA also said conventional oil is acceptable if it meets the manufacturer’s specification.
Choose by your manual first. Synthetic is the better fit for turbocharged engines, towing, extreme temperatures and long intervals.
Key differences
| Conventional | Full synthetic | |
|---|---|---|
| Base oil | Refined from crude oil | Engineered base stocks, often PAO or other synthetics |
| Cold-start flow | Good | Generally better |
| Heat and oxidation resistance | Adequate | Generally better |
| Cost per change | Lower | Higher |
| Change interval | Shorter, per manual | Often longer, per manual and driving |
Synthetic blends sit in between. See full synthetic vs synthetic blend and what synthetic oil is made from.
What the AAA study found
AAA tested five 5W-20 synthetic oils and their conventional equivalents in eight ASTM-based tests covering deposits, low-temperature performance and oxidation. Synthetics performed an average of 47% better. AAA did not test blends, and it did not say conventional oil is bad, only that synthetic offers more protection.
Switching to synthetic? Preferred Customers buy AMSOIL synthetic about 25% below suggested retail.
When to choose each
- Use synthetic for turbocharged or direct-injection engines, towing, stop-and-go driving, very hot or cold climates, and where your manual requires it.
- Conventional can be fine for older, low-stress engines if it meets your manual’s specification and you follow the interval.
- Never choose by price alone. Check viscosity and approvals using our oil label guide.
Can you mix them?
Different oils are generally compatible, but mixing dilutes the benefits. See what happens if you mix engine oils before topping off.
Synthetic vs conventional FAQ
Is synthetic oil worth the extra cost?
Often yes, for the added protection and longer intervals, but follow your manual and driving conditions.
Can I switch from conventional to synthetic?
Yes, in most engines. Keep the same viscosity and follow your manual.
Does synthetic oil last longer?
It can, but follow the interval for your vehicle and oil.
Does synthetic oil void my warranty?
Not by itself, if it meets the manufacturer’s specification.
Is full synthetic the same as synthetic blend?
No. Blends mix synthetic and conventional base oils. Read the label.
Upgrade to synthetic for less
AMSOIL Preferred Customer membership is $20/year (or a $10 six-month trial), with free shipping on orders of $100 or more.
Sources (checked Oct 3, 2026): AAA: synthetic vs conventional oil · AAA Oregon/Idaho: study summary · AMSOIL blog: synthetic vs conventional
AMSOIL is a registered trademark of AMSOIL INC. LubeOilSales.com is operated by Alan Williams, an independent AMSOIL Dealer (Dealer #1243776), and is not owned or endorsed by AMSOIL INC. If you join through my links, I may earn a commission at no extra cost to you. This guide is general information. Follow your owner’s manual and consult a qualified professional when in doubt. Content last reviewed October 3, 2026.