Why not use synthetic oil?

Synthetic oil isn’t automatically the best choice for every vehicle or budget. It can cost more, may not be necessary for older engines, and some warranties or manufacturer guidelines still favor conventional oil in certain cases.

The decision to use or skip synthetic oil hinges on how your engine was designed, how you drive, and the climate you operate in. This article examines the practical considerations, common caveats, and situations where synthetic oil may or may not be the right fit.

What synthetic oil is and how it compares to conventional oil

Oil comes in several forms. Conventional or mineral oil is derived directly from refined crude and is suitable for many engines when changed at manufacturer-recommended intervals. Synthetic oil is chemically engineered to resist breakdown, perform better at extreme temperatures, and often last longer between changes. A synthetic blend sits between the two, combining conventional oil with some synthetic components. Understanding these differences helps explain why some people choose not to use synthetic oil in certain circumstances.

Reasons some drivers avoid synthetic oil

Here is a concise look at practical drawbacks cited by motorists and technicians when considering synthetic oil alternatives.

• Higher upfront and ongoing costs: Full synthetic oil typically costs more per quart than conventional oil, and some vehicles require more expensive filtering or service plans to maintain the benefits.


• Engine compatibility and seals: In some older engines, switching to full synthetic can reveal or exacerbate leaks by removing sludge deposits that were helping seals, or by altering how deposits are cleaned inside the engine. This is not universal, but it’s a reason to consult a mechanic if you’re changing oil types in an older or high-mileage motor.


• Warranty and manufacturer guidelines: Many new-vehicle warranties and maintenance programs specify a particular oil type and viscosity. Using oil not endorsed by the manufacturer can affect coverage or require proof of adherence to the recommended schedule.


• Maintenance and drain intervals that don’t align with reality: Synthetic oils enable longer service intervals in some cases, but real-world driving (short trips, extreme temps, heavy loads) can reduce the expected benefits. If you don’t actually extend changes, you may not gain cost efficiency.


• Environmental and production considerations: Some critics point to the higher energy and resource use in producing synthetic oils compared with conventional oils, as well as disposal considerations. For drivers weighing environmental impact, this can factor into the decision.

In practice, the decision to skip synthetic oil often comes down to budget, engine type, and adherence to manufacturer guidance. Consulting your vehicle’s manual and a trusted mechanic can help determine whether conventional oil is adequate for your situation.

When synthetic oil makes sense

There are clear scenarios where synthetic oil delivers tangible benefits and is commonly recommended by manufacturers and professionals.

• High-performance or turbocharged engines: These engines often run hotter and under harder loads, where synthetic oil’s stability and protection can reduce wear and extend engine life.


• Extremely cold or hot climates: Synthetic oil flows more readily in cold starts and maintains viscosity at high temperatures, improving protection during temperature extremes.


• Long-distance or demanding use: Vehicles used for towing, aggressive driving, or long highway trips may benefit from the longer drain intervals and robust protection synthetic oils provide.


• New or modern engines with OEM recommendations: If the manufacturer calls for synthetic or a synthetic blend, following that guidance is the safest path to maintain warranty and performance.

If your driving profile matches these scenarios, the economics and performance gains of synthetic oil can outweigh the higher price. Always verify with the owner’s manual and a qualified technician.

Practical tips for choosing between oil types

To make an informed choice, consider the following practical steps and questions before you decide which oil to use.

• Check the owner’s manual for the recommended oil type, viscosity, and drain interval. Follow the manufacturer’s instructions as the baseline for your vehicle.


• Assess your climate and driving patterns: frequent short trips, heavy towing, or extreme temperatures may influence whether synthetic oil is advantageous.


• Evaluate engine age and condition: high-mileage or older engines may respond differently to switching oil types. A mechanic can help assess potential leak risks or gasket concerns.


• Consider warranty implications: if your vehicle is under warranty, ensure that the oil type and change schedule align with the terms to avoid coverage issues.

Making an informed choice involves balancing cost, maintenance practicality, and the specific needs of your engine. If in doubt, a professional opinion tailored to your car and locale is worth obtaining.

Summary

Synthetic oil offers advantages like improved high-temperature stability, better cold-start performance, and longer change intervals in many modern engines. However, it is not universally necessary or the most economical choice. Costs, potential compatibility issues with older engines, and warranty considerations mean conventional oil remains a sensible option for a broad range of vehicles and drivers. The best approach is to follow the manufacturer’s guidance, weigh your driving needs, and consult a trusted mechanic when contemplating a switch.

Will synthetic oil damage a high mileage engine?

No, modern synthetic oil will not damage a high-mileage engine, and it can actually be beneficial. The old myth that switching to synthetic would cause leaks is outdated; modern synthetics have detergent additives that clean out sludge and seal conditioners to protect seals, while high-mileage synthetic blends offer even more protection for older engines. 
Why the "damage" myth is false

• Seal compatibility: Early synthetic oils were sometimes cited as being too "slipperier" and could cause leaks in older seals. However, modern synthetic oils contain additives that protect and condition seals, and many are now blended with a high-mileage oil formula specifically to prevent issues. 
• Sludge buildup: Conventional oils can leave behind sludge in an engine over time. When switching to synthetic oil, the detergents can clean this sludge away, potentially revealing existing leaks or causing temporary oil burning. However, this is a sign of the engine's condition, not a failure of the synthetic oil itself. 
• Modern formulas: Today, most oils labeled "high mileage" are synthetic or synthetic blends and contain seal conditioners that can actually help reduce oil consumption in older engines. 

What to do when switching

• Use a high-mileage formula: For the best results, choose a synthetic oil specifically formulated for high-mileage engines. These contain extra seal conditioners. 
• Check for leaks: Before switching, it's wise to check for existing leaks. The cleaning action of synthetic oil might reveal a problem with a worn-out seal, but it doesn't cause the problem itself. 
• Consult the owner's manual: If you're unsure, consult your car's owner's manual or an experienced mechanic for the best type of oil for your specific engine. 

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

Yes, synthetic oil is generally better than conventional oil because it offers superior engine protection, lasts longer between changes, and performs better in extreme temperatures. While synthetic oil is more expensive, its benefits include better lubrication, enhanced durability, and a cleaner engine due to special additives. 
Synthetic oil advantages

• Better protection: Synthetic oil is chemically engineered to provide superior lubrication and protection, especially under high stress or load like towing or in high-stress conditions. 
• Longer life: It does not break down as quickly as conventional oil, allowing for longer intervals between oil changes (potentially 6,000-7,500 miles or more). 
• Improved performance in temperature extremes: It flows better at low temperatures for easier start-ups and maintains viscosity better at high temperatures, protecting your engine in both hot and cold climates. 
• Cleaner engine: Synthetic oils contain powerful additives that help prevent sludge buildup, keep pistons cleaner, and reduce deposits in the engine. 

Conventional oil advantages

• Lower cost: The most significant advantage is the lower price, making it a more budget-friendly option upfront. 
• Effective with frequent changes: Conventional oil works fine and is effective when you follow the recommended oil change schedule for your vehicle. 

Which one should you choose?

• Follow your owner's manual: The best practice is to use the type of oil your vehicle's manufacturer recommends. Many modern, high-tech engines require synthetic oil. 
• Consider your driving conditions: If you frequently drive in extreme hot or cold weather, or put your vehicle under high stress, synthetic oil is a better choice. 
• Evaluate the long-term cost: While synthetic oil is more expensive per change, the longer intervals and potential for reduced engine wear can make it a cost-effective choice in the long run. 

Is there a reason to not use synthetic oil?

Synthetic oils seem to exploit gaps in metal that conventional does not which leads to leaks in certain, usually older, vehicles. Also when breaking in a new engine you want the rings to seat and synthetic oil tends to be too slick and resistant to breakdown.

What happens if you put regular oil and not synthetic?

Putting conventional oil in a car that requires synthetic oil can lead to a loss of performance, increased engine wear over time, and potentially voiding the manufacturer's warranty. While it's not an immediate disaster and the oils can be mixed, conventional oil doesn't offer the same protection against heat, cold, or breakdown as synthetic, requiring more frequent oil changes to compensate. 
Potential consequences

• Reduced engine protection: Conventional oil is not engineered to withstand the same extreme temperatures or last as long as synthetic oil, potentially leading to increased wear. 
• Performance issues: The engine may perform less efficiently, and you could experience slower cranking in cold weather because conventional oil takes longer to reach its optimal viscosity. 
• Shorter oil life: You will need to change the conventional oil much more frequently (every 3,000-5,000 miles) compared to the extended intervals of synthetic oil (10,000-15,000 miles). 
• Voided warranty: Using the wrong type of oil can void your new car's warranty, as it can be considered a failure to follow the manufacturer's specifications. 
• Engine cleaning issues: While mixing is not harmful, the lower quality of conventional oil means it may not clean the engine as effectively and can lead to more sludge buildup over time. 

What to do

• Use the correct oil: Always refer to your owner's manual or the oil filler cap to see the exact specifications your engine requires. 
• Check for warnings: Look for a warning on the oil cap or in your manual that specifically states synthetic oil is required. 
• Consult a mechanic: If you've already used conventional oil, consult a trusted mechanic to see what the best course of action is. It may be best to switch back to synthetic oil as soon as possible.