Which is better: synthetic or fully synthetic oil?

Fully synthetic oil generally delivers better protection and performance than synthetic blend oil, especially in extreme temperatures, turbocharged or direct-injection engines, and when longer drain intervals are desired—provided it meets your vehicle’s exact specifications and approvals. The catch: “synthetic” on the label can mean different things depending on market and branding, so the best choice is the one that meets your owner’s manual requirements and relevant certifications.

What the labels really mean

Automakers and oil companies use overlapping terms that can confuse shoppers. Understanding how the industry labels engine oil helps you choose confidently.

• Conventional (mineral) oil: Refined from crude, with additive packages but less advanced base stocks and narrower performance envelope.
• Synthetic blend (semi-synthetic): A mix of conventional and synthetic base oils. Often labeled “synthetic” in casual conversation, but not “full” or “fully” synthetic. Offers a step up in stability and cleanliness at a lower price than full synthetic.
• Fully synthetic (full synthetic): Uses synthetic base stocks (commonly Group III/III+ hydroisomerized or Group IV PAO, sometimes with Group V esters) plus advanced additives for superior high/low temperature performance, deposit control, and volatility.
• Labeling realities: In the U.S., many “full synthetic” oils are high-quality Group III/III+ and perform excellently; in Europe, stricter OEM approvals often govern what qualifies for extended drains. Whether Group III or Group IV, real-world results depend as much on the additive package and approvals as on the base oil.

The takeaway: “Fully synthetic” generally denotes the top tier, while “synthetic blend” is a mid-tier option. Look beyond the marketing to the specifications your vehicle requires.

How they perform side by side

Engine oils are judged on cold-start behavior, high-temperature stability, cleanliness, volatility, and compatibility with modern engines. Here’s where fully synthetic typically outperforms blends.

• Cold starts: Full synthetics flow better at low temperatures (e.g., 0W grades), reducing start-up wear and aiding fuel economy.
• High-temperature stability: Better resistance to oxidation and shear at sustained high loads/heat—valuable for turbocharged, towing, track, or desert driving.
• Cleanliness: Superior deposit control keeps rings, turbo bearings, and variable valve timing systems cleaner, helping maintain performance.
• Volatility: Lower NOACK evaporation helps reduce oil consumption and intake valve deposits in GDI/turbo engines.
• Fuel efficiency: Lower internal friction and optimized viscosity modifiers can improve MPG marginally versus blends.
• Longer drain potential: Many full synthetics are formulated for extended oil-change intervals when the oil meets the vehicle maker’s long-life approvals.
• Modern engine safety: Quality full synthetics meeting API SP/ILSAC GF-6 and OEM specs offer strong protection against LSPI (low-speed pre-ignition) and timing chain wear in turbo GDI engines.

For most late-model vehicles, these advantages make full synthetic the stronger all-around choice, particularly under harsh conditions or with advanced engine technology.

When a synthetic blend can be enough

A synthetic blend may be appropriate in certain scenarios, provided it meets the automaker’s specification and is changed on schedule.

• Budget-focused maintenance: Blends often cost less while still improving on conventional oil’s heat and oxidation performance.
• Older, non-turbo engines with modest demands: If the OEM spec doesn’t require full synthetic, a blend changed at conservative intervals can be adequate.
• Short-trip, temperate climates: In mild use without extreme cold or heat, the tangible benefits of full synthetic may be smaller.
• Fleet or high-frequency service: If you’re changing oil frequently due to duty cycle, the extra longevity of full synthetic may matter less.

Even in these cases, verify the oil meets your vehicle’s required certifications; if costs are close, the added protection of full synthetic is still a prudent upgrade.

What to look for on the label

Choose by specification and approval first, then by brand or marketing term. These markings are more important than “blend” vs “full synthetic.”

• API and ILSAC: For gasoline engines, look for API SP and ILSAC GF-6A/GF-6B (GF-6B applies to certain 0W-16 oils). These address LSPI, wear, deposits, and chain protection.
• ACEA sequences (Europe): A3/B4, A5/B5, A7/B7, C3, C5, C6—your manual or filler cap usually specifies which is required.
• OEM approvals: Examples include GM dexos1 Gen 3 (gasoline), VW 504 00/507 00, BMW Longlife-01/LL-17 FE, Mercedes-Benz 229.5/229.52, Porsche A40/C30. For diesels, look for API CK-4 or FA-4 and relevant OEM specs.
• Viscosity grade: Match the recommended grade (e.g., 0W-20, 5W-30, 0W-40) for your climate and engine.
• Special applications: Motorcycles with wet clutches require JASO MA/MA2; some DPF-equipped diesels need low-SAPS “C” category oils.

If the bottle matches your required spec and approvals, it’s suitable; between two compliant oils, the full synthetic option typically offers the strongest margin of protection.

Cost and oil-change intervals

Full synthetic usually costs more per quart, but can be more economical over time if your vehicle supports longer intervals. Many modern vehicles with oil life monitors can safely run 7,500–10,000 miles (12,000–16,000 km) on approved full synthetics; certain European long-life approvals allow longer intervals when conditions and monitoring permit. Always follow your owner’s manual and oil-life monitor. Severe service (frequent short trips, heavy towing, extreme temperatures, dusty environments) warrants shorter intervals regardless of oil type.

Myths and edge cases

A few persistent misconceptions can muddy the decision. Here’s what the evidence and modern formulations support.

• “Full synthetic causes leaks”: Modern synthetics don’t “cause” leaks; they may reveal existing seal issues because they clean deposits. High-mileage synthetics include seal conditioners to mitigate seepage.
• “You can’t switch back and forth”: Mixing compatible oils that meet the same spec is safe, though ideally you use one product consistently and top up with the same or equivalent specification.
• “Older engines can’t use synthetic”: Many can, as long as viscosity and specifications are correct. For very old or worn engines, a high-mileage full synthetic or blend can be beneficial.
• “Full synthetic always extends intervals”: Only if the oil also carries the required OEM long-drain approval and your usage pattern supports it.
• Special cases: Performance/turbo cars, hybrids with frequent start-stop, and GDI engines benefit markedly from full synthetics that meet API SP and the relevant OEM approvals; motorcycles and certain racing applications have unique needs—follow JASO or motorsport guidance.

In short, compatibility and approvals trump myths; tailor the choice to your engine, usage, and manufacturer requirements.

Bottom line

Fully synthetic oil is generally “better” than a synthetic blend in measurable ways—cold-flow, high-heat stability, cleanliness, volatility, and potential longevity. If it meets your vehicle’s specifications and fits your budget, it’s the safer bet for most modern engines. If a blend meets the required standards and your driving is mild with regular changes, it can be a sensible, cost-effective choice. Always choose by the specs in your owner’s manual first, then decide between full synthetic and blend.

Summary

Fully synthetic oils typically outperform synthetic blends and are preferable for modern, turbocharged, or high-stress engines and for longer drain intervals—provided they meet your vehicle’s specs (API SP/ILSAC GF-6, ACEA, and OEM approvals). Synthetic blends can suffice for older, lightly used engines if they meet the same specs and are changed on schedule. The best oil for your car is the one that matches the manufacturer’s approvals and viscosity recommendations; between two compliant options, full synthetic offers the strongest protection margin.

What is the disadvantage of fully synthetic engine oil?

Perhaps the biggest disadvantage to synthetic oil is the price. Many blends can cost twice as much as their conventional counterparts. And considering that many vehicles will run fine on semi-synthetic/conventional motor oil, the additional cost can be a major prohibiting factor.

Which oil is best, synthetic or fully synthetic?

For most modern vehicles, fully synthetic oil is the recommended choice due to its superior performance and long-term benefits.

Is 100% synthetic the same as fully synthetic?

The oil could use 90% Group IV and 10% Group III base oil; or, it could use 90% Group III and 10% Group IV base oils. As long as it only uses Groups III, IV or V base oils, it’s a synthetic oil. That being the case, the terms “100% synthetic” and “full synthetic” describe the same thing.

Should I get synthetic oil or full synthetic?

Synthetic oil will help your vehicle’s low temperature performance. As well, it can help with your vehicle’s oil shear stability and possesses higher heat resistance and thermal stability. Most importantly, full synthetic will provide better oil burn performance.