Synthetic vs. Conventional Oil: What's the Difference?

Engine oil is essential for keeping a vehicle's engine properly lubricated. It reduces friction between moving parts, helps carry heat away, suspends certain contaminants, and protects metal surfaces from wear and corrosion.

When shopping for motor oil, drivers often have to choose between conventional, synthetic blend, and full synthetic products. The bottles may look similar, but the oils can differ in their base stocks, additive formulations, performance characteristics, and prices.

So, is synthetic oil always better? Not necessarily for every vehicle or every driver. Understanding the differences can help you choose the correct oil without paying for features your vehicle may not require.

What Is Conventional Motor Oil?

Conventional motor oil is made primarily from refined petroleum-based base oils combined with additives. These additives help the oil resist oxidation, control deposits, reduce wear, and perform under the conditions for which it was formulated.

Conventional oil has been used in automotive engines for many years and can provide appropriate protection when it meets the engine manufacturer's requirements and is changed at the recommended interval.

It is often less expensive than full synthetic oil. However, it may not provide the same performance characteristics as some synthetic products under extreme temperatures or demanding operating conditions.

What Is Synthetic Motor Oil?

Synthetic motor oil is formulated using base oils and additives selected or processed to provide specific performance characteristics. Full synthetic products are designed to deliver reliable lubrication across a range of operating conditions.

Depending on the formulation, synthetic oil may offer improved resistance to oxidation, more consistent viscosity behavior across temperature changes, and better protection against deposits compared with some conventional oils.

Synthetic oil is commonly specified for many modern engines, including some turbocharged engines that operate under high temperatures and pressures. However, the label "synthetic" alone does not guarantee that a product meets the requirements of every engine.

Synthetic vs. Conventional Oil: Key Differences

Both types of oil lubricate the engine, but their performance can differ depending on the base oil, additive package, viscosity grade, and applicable industry standards.

These are general comparisons, not guarantees for every product. A high-quality conventional oil that meets the required specification may be more appropriate for a particular engine than a synthetic oil with the wrong viscosity or approval.

Benefits of Synthetic Oil

1. Better Performance in Cold Weather

Engine oil becomes more viscous as temperatures drop. Many synthetic oils are formulated to flow effectively at low temperatures, helping the lubrication system supply oil during cold starts.

Cold-weather performance still depends on the oil's viscosity grade. For example, the winter rating in a multigrade oil such as 0W-20 or 5W-30 provides information about its low-temperature performance. Always use a grade approved for your engine.

2. Resistance to Oxidation and Heat

Engine oil is exposed to heat and oxygen during operation. Over time, these conditions can cause oil to oxidize and degrade. Many synthetic formulations are designed to resist oxidation and maintain their properties under demanding conditions.

This can be especially useful in vehicles that experience high engine temperatures, frequent stop-and-go traffic, towing, or other demanding operating conditions, provided the oil meets the manufacturer's specifications.

3. Potentially Better Deposit Control

Quality synthetic oils contain additives designed to help control sludge, varnish, and other deposits. The result depends on the entire formulation, including the detergent and dispersant additives, rather than the synthetic label alone.

4. Suitable for Many Modern Engines

Many modern engines are designed around specific synthetic oil formulations and industry or manufacturer approvals. Turbocharged engines, in particular, may require oils that meet precise performance standards.

Check the owner's manual for the exact viscosity grade and specification. Do not choose an oil based only on its price or the words "full synthetic" on the bottle.

Are There Any Disadvantages to Synthetic Oil?

Higher Purchase Price

Full synthetic oil usually costs more per quart than conventional oil. The difference may be worthwhile if your vehicle requires synthetic oil or if its performance characteristics suit your driving conditions.

However, paying more does not automatically mean that an oil is right for your engine. The required specification and viscosity grade should come first.

It Does Not Eliminate Maintenance

Synthetic oil still ages, becomes contaminated, and eventually needs to be changed. It cannot compensate for a neglected engine, a serious oil leak, a faulty oil filter, or another mechanical problem.

Continue checking the oil level and following the maintenance schedule even if you use a premium synthetic product.

What Is Synthetic Blend Oil?

Synthetic blend oil combines synthetic base oils with conventional base oils and additives. It is often positioned between conventional and full synthetic products in terms of price and intended performance.

A synthetic blend may be a suitable choice when it meets the vehicle manufacturer's requirements. However, the term "blend" does not identify one universal formulation, so compare the viscosity grade and performance specifications on the label.

If your owner's manual requires a particular full synthetic oil or manufacturer approval, do not substitute a blend unless it explicitly meets those requirements.

Can You Switch from Conventional to Synthetic Oil?

In most vehicles, switching from conventional to synthetic oil is acceptable if the new oil has the correct viscosity grade and meets the required specifications. There is generally no need for a special flushing procedure simply because you are changing oil types.

If your engine is older, has a history of oil leaks, or consumes oil, check its condition and follow the manufacturer's recommendations before making changes. Switching to synthetic oil does not automatically repair existing leaks or mechanical wear.

You can also switch back to conventional oil in an engine that permits it, provided the oil meets all required specifications. However, do not use conventional oil if the manufacturer specifically requires a synthetic product or approval that the conventional oil does not meet.

Does Synthetic Oil Last Longer?

Some synthetic oils can maintain their performance longer under certain conditions than conventional oils. However, that does not mean every synthetic oil can safely be used for an extended interval in every vehicle.

The correct oil change interval depends on the vehicle, engine design, oil specification, driving conditions, and the manufacturer's maintenance schedule. Frequent short trips, heavy traffic, towing, extreme temperatures, and other severe conditions may require more frequent service.

If your vehicle has an oil-life monitoring system, follow the manufacturer's instructions for interpreting it. Do not extend oil changes beyond the permitted interval simply because the bottle says "synthetic."

How to Choose the Right Oil for Your Car

Choosing engine oil involves more than deciding between conventional and synthetic. Use the following steps to make a suitable choice for your vehicle.

1. Check the Owner's Manual

Find the recommended viscosity grade and any required industry standards or manufacturer approvals. If the manual is unavailable, check the manufacturer's official service information for your specific model and engine.

2. Match the Viscosity Grade

Viscosity grades such as 0W-20, 5W-20, and 5W-30 describe how an oil performs under specified temperature conditions. These grades are not interchangeable in every engine.

Do not switch to a thicker or thinner oil simply because you believe it will protect an older engine better. Use only a grade permitted by the manufacturer.

3. Check the Required Specifications

Some engines require oil that meets a particular API or ILSAC standard, an ACEA specification, or a vehicle manufacturer's own approval. The exact requirements vary by vehicle and engine.

Make sure the oil product explicitly meets the applicable requirements. Similar viscosity grades do not necessarily mean two oils provide the same performance or approval.

4. Follow the Recommended Change Interval

Use the service interval specified by the manufacturer, including any shorter interval required for severe driving conditions. Check the oil level periodically and investigate unexpected oil loss.

Is Synthetic Oil Worth the Extra Cost?

Synthetic oil can be worth the extra cost when your vehicle requires it, when its performance characteristics suit your climate and driving conditions, or when the manufacturer specifies a synthetic formulation.

If your vehicle permits conventional oil and the product meets all required specifications, conventional oil may also provide suitable protection when maintained correctly.

The best choice is not necessarily the most expensive oil. It is the oil that meets your engine's requirements and is changed according to the correct maintenance schedule.