Which Lasts Longer: Synthetic or Conventional Oil?

Synthetic oil generally lasts longer than conventional oil, often supporting oil change intervals of about 7,500–10,000 miles (or up to one year) under normal driving, compared with roughly 3,000–5,000 miles (or about six months) for conventional oil. That said, you should always follow your vehicle’s owner’s manual and oil-life monitor because engine design, driving conditions, and warranty requirements ultimately set the safe interval.

Why Synthetic Oil Typically Lasts Longer

Modern synthetic oils are engineered with more uniform base molecules and advanced additive packages that resist heat, oxidation, and viscosity breakdown better than conventional mineral-based oils. This chemistry helps synthetics maintain protective film strength longer, reducing deposits and wear over extended drain intervals.

• More stable base stocks: Group III/IV/V synthetic bases offer superior thermal and oxidative stability versus conventional mineral oils.
• Lower volatility: Reduced evaporation (lower NOACK) helps keep viscosity in spec and cuts oil consumption at high temperatures.
• Stronger additive systems: Detergents, dispersants, and antioxidants in synthetics are formulated for longer service and cleaner engines.
• Shear stability: Better resistance to viscosity loss under mechanical stress keeps protection consistent between changes.
• Improved cold flow: Faster lubrication on cold starts reduces wear, helping preserve oil performance over time.
• Deposit and sludge control: Enhanced resistance to oxidation and fuel dilution helps prevent varnish and sludge formation.

Taken together, these characteristics allow synthetics to maintain protective properties over more miles and months, especially under mixed driving conditions.

Typical Oil Change Intervals

Intervals vary by vehicle, oil specification, and driving profile. The figures below reflect common ranges in North America for modern passenger vehicles; always defer to the owner’s manual and the vehicle’s oil-life monitoring system if equipped.

1. Conventional oil: About 3,000–5,000 miles or 3–6 months, shorter under severe service (frequent short trips, heavy idling, extreme heat/cold).
2. Synthetic blend: Roughly 5,000–7,500 miles or up to 6–12 months, depending on OEM guidance.
3. Full synthetic: Commonly 7,500–10,000 miles or up to 12 months for normal service; some vehicles and oils may safely reach 10,000–12,000 miles when the OEM allows it.
4. Extended-performance synthetics: Certain products and European long-life specifications can span up to 15,000 miles or 20,000–30,000 km under manufacturer oil-life systems; only follow these intervals if your vehicle explicitly supports them.

These ranges are guidelines, not guarantees. Short trips, turbocharged direct injection, towing, dust, and extreme climates can reduce safe intervals significantly.

What Automakers Recommend Today

Many newer vehicles are factory-filled with synthetic oil and rely on an oil-life monitor that adjusts intervals based on real-world use. Typical recommended intervals for modern cars land between 7,500 and 10,000 miles or one year for normal driving, with shorter intervals for severe service. Some European vehicles using approved long-life oils may allow longer intervals governed by their service monitors. If your vehicle is under warranty, adhere to the manual’s viscosity grade and service specifications.

Factors That Shorten or Extend Oil Life

How and where you drive often matters more than the label on the bottle. The following factors can significantly affect how long your oil remains effective.

• Driving profile: Frequent short trips and stop‑and‑go driving prevent full warm-up, promoting moisture and fuel dilution.
• Turbocharged/direct-injection engines: Higher heat and potential fuel dilution stress oil; some require tougher specs and shorter intervals.
• Load and environment: Towing, hauling, mountain grades, dusty conditions, and extreme temperatures accelerate degradation.
• Oil capacity and engine design: Larger sumps and engines designed for long drains can safely run longer intervals with the right oil.
• Maintenance condition: A healthy PCV system and a quality oil filter extend oil life; coolant or fuel leaks rapidly destroy it.
• Time in service: Even without mileage, additives deplete and moisture accumulates; many OEMs cap intervals at 12 months.

Considering these factors alongside your oil-life monitor provides a realistic interval tailored to your specific usage.

Synthetic vs. Synthetic Blend vs. High‑Mileage Oils

Not all “synthetics” are the same, and the right choice depends on your engine’s needs, age, and manufacturer specifications.

• Full synthetic: Highest stability and longest potential intervals; best for modern engines, turbos, and extreme climates.
• Synthetic blend: Middle ground offering better protection than conventional at a lower price than full synthetic.
• High‑mileage oil: Formulated (often in synthetic blends or full synthetic) with seal conditioners and additives for engines typically over ~75,000 miles.

Regardless of type, ensure the oil meets the exact specifications your automaker calls for before considering extended intervals.

Warranty, Specifications, and Oil-Life Monitors

“Lasts longer” only matters if the oil meets the standards your engine requires. Modern gasoline engines commonly specify API SP and ILSAC GF‑6 (GF‑6A or GF‑6B for low-viscosity grades), and many automakers add their own approvals (for example, GM dexos1 Gen 3). Oil-life monitors integrate temperature, load, and drive-cycle data to time changes more accurately than mileage alone.

• Use the exact viscosity and specifications in your owner’s manual, especially during warranty.
• Follow your oil-life monitor or manual’s time/mileage cap—whichever comes first.
• Keep receipts and records showing the oil met the required specs.
• Choose a high-quality filter rated for the intended interval; some extended drains require extended-life filters.

Meeting the right spec and respecting the oil-life system ensures longevity without risking engine health or warranty coverage.

Bottom Line

Synthetic oil almost always lasts longer than conventional oil because it resists heat, oxidation, and shear more effectively. In practice, that translates to longer, safer intervals—provided the oil meets your vehicle’s specifications and your driving patterns aren’t unusually severe. When in doubt, follow the owner’s manual and the oil-life monitor.

Summary

Synthetic oil outlasts conventional oil in most scenarios, commonly enabling 7,500–10,000‑mile or annual intervals versus 3,000–5,000 miles for conventional. Real-world interval length depends on your vehicle’s requirements, driving conditions, and adherence to standards like API SP/ILSAC GF‑6 and any OEM approvals. Trust your owner’s manual and oil-life monitor to set the safest schedule.

What is the disadvantage of synthetic oil?

The primary disadvantages of synthetic oil are its higher cost and the potential for it to cause leaks or smoking in older or worn engines because it’s a more effective solvent than conventional oil, which can dislodge old sludge and deposits that were sealing leaks or keeping rings clean. Additionally, while not a major issue for most modern cars, synthetic oil is not always necessary for standard engines and may offer only slightly less fuel economy at highway speeds in some multi-grade oils. 
Higher Cost: 

• Synthetic oils are generally two to four times more expensive than conventional motor oils. This added cost can be a significant factor for drivers on a tight budget, making it a notable downside.

Compatibility and Performance Issues in Older Engines:

• Engine leaks: Synthetic oil’s superior cleaning properties can dislodge accumulated sludge and deposits in older engines, potentially revealing or worsening existing leaks in worn gaskets and seals. 
• Smoking: In some cases, the cleaning action of synthetic oil can dislodge deposits from piston rings or valve stem seals, leading to increased oil consumption and resulting in blue smoke from the exhaust. 
• Not for every engine: Not all engines are designed to use synthetic oil, especially older or high-mileage engines. It’s crucial to check your vehicle’s owner’s manual before switching. 

Potential for Overkill and Slight Fuel Economy Reduction: 

• For engines operating under normal conditions, full synthetic oil may be unnecessary, making it an expensive “overkill”. 
• Some multi-grade synthetic oils might show a slightly lower fuel economy at highway speeds compared to conventional oils, as mineral oils typically use more viscosity index improvers. 

Sludge Buildup in Older Engines: 

• If you switch a very dirty engine to synthetic oil without first removing the existing sludge, the aggressive cleaning action of the synthetic oil can quickly load up the oil and filter, potentially causing problems. It’s often recommended to use an engine flush and change the oil filter before switching to synthetic in such cases.

When should you not use full synthetic oil?

Better For Older Engines
This being said, however, it is still not recommended to use synthetic oil in engines that have experienced significant actions – specifically, those that have reached around 75,000 miles on the odometer.

Does synthetic oil last longer than conventional oil?

Yes, synthetic oil lasts significantly longer than conventional oil due to its refined molecular structure, resistance to breakdown, and ability to withstand higher temperatures and extreme conditions. While conventional oil typically needs changes every 3,000-5,000 miles, full synthetic oil can extend oil change intervals to 7,500-12,000 miles or even longer, depending on the specific oil and manufacturer recommendations. 
Why Synthetic Oil Lasts Longer

• Fewer Impurities: Synthetic oil starts with a less refined crude oil and undergoes more intensive refining and artificial production, resulting in fewer impurities and a more uniform molecular structure. 
• Better Thermal Stability: Synthetic oil resists thermal breakdown and evaporation at higher temperatures, which is a major cause of degradation in conventional oils. 
• Improved Additives: Synthetic oils contain higher quality additives, including cleansers and anti-oxidizers, that keep the oil performing well for longer periods and help maintain engine cleanliness. 
• Better Viscosity: The more stable molecular structure of synthetic oil allows it to maintain better viscosity, or flow, in a wider range of temperatures, providing better protection in both hot and cold climates. 

Benefits of Longer Intervals

• Reduced Maintenance: Longer intervals mean fewer trips to the mechanic for oil changes, which can be a significant time and cost saver. 
• Improved Engine Performance: By resisting sludge and deposit formation, synthetic oil helps keep the engine cleaner, improving performance and longevity. 
• Better Protection: Synthetic oil provides superior lubrication, especially in high-performance or extreme-condition vehicles, by flowing smoothly and reducing friction. 

Which is better for your engine, synthetic or conventional oil?

Yes, synthetic oil is generally better than regular (conventional) oil because it offers superior engine protection, performs better in extreme temperatures, and can extend oil change intervals, leading to a cleaner, more efficient, and longer-lasting engine. It is made with a more uniform molecular structure and enhanced additives, which provide better lubrication, prevent sludge buildup, and reduce wear more effectively than conventional oil. 
Key Advantages of Synthetic Oil

• Enhanced Engine Protection: Opens in new tabSynthetic oil’s stable molecular structure resists breakdown, providing better protection against wear, friction, and contaminants, resulting in a cleaner engine and reduced sludge formation. 
• Improved Performance in Extreme Temperatures: Opens in new tabIt flows better in cold weather and doesn’t break down as quickly in high heat, offering superior lubrication and cooling performance across a wider range of temperatures. 
• Longer Oil Change Intervals: Opens in new tabDue to its stability and resistance to contamination, synthetic oil lasts longer than conventional oil, allowing for extended oil change intervals (e.g., 6,000-7,500 miles or more) compared to traditional oil’s shorter intervals (e.g., 3,000 miles). 
• Better Fuel Economy: Opens in new tabWith its superior lubricating properties and efficiency, synthetic oil can contribute to improved engine efficiency and better fuel economy. 

When to Use Synthetic vs. Conventional Oil

• Modern and High-Performance Engines: Opens in new tabSynthetic oil is ideal for modern, complex engines and high-performance vehicles that demand the best protection and efficiency. 
• Severe Driving Conditions: Opens in new tabUsing synthetic oil is beneficial for vehicles that experience frequent short trips, towing, or are operated in extreme hot or cold climates. 
• Older Engines: Opens in new tabWhile conventional oil can work for simpler engines, synthetic oil can also be a good choice for older vehicles to help prevent sludge buildup and reduce wear on aging components. 

Considerations

• Cost: Synthetic oil is generally more expensive than conventional oil due to the advanced refining and manufacturing processes involved. 
• Manufacturer Recommendations: Always check your vehicle’s owner’s manual to see the type of oil recommended by the manufacturer.