The difference between semi-synthetic and “real” synthetic oil

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The difference between semi-synthetic and “real” synthetic oil

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What is the difference between a semi-synthetic motor oil and a synthetic motor oil?

A mineral oil, or conventional motor oil, is an oil that is refined or extracted through other means from crude oil. Crude oil is composed of a great number of differing hydrocarbon structures, each having their own characteristics—some of which are not helpful for lubrication and considered contaminants.

For example, mineral oils contain wax that needs to be minimized or removed. Wax works great in candles but not in a motor oil. The objective in refining is to remove these contaminants and separate the hydrocarbon structures into groups that possess desirable properties. Therefore, a mineral or conventional oil is a refined mineral oil product that has been “cleaned up” to serve as a lubricant.

Today, mineral based oils are being refined into products that are superior to those available only a few years ago. Despite progress made in the performance characteristics of mineral oils, advances in the design and operation of equipment have led to problems relating to inadequate lubricant performance. Thus, there is a need for something better.

A synthetic motor oil is a lubricant that is designed, not refined—that is, desired performance characteristics are designed into the synthetic lubricant to provide enhanced features and benefits. Compared to a mineral oil, full synthetic motor oils have a wider operational temperature range (performing well at lower temperatures as well as high temperatures), better shear stability, lower toxicity, lower deposit formation and are less volatile while still being compatible with mineral oils. Synthetic oils also have different oil change intervals than conventional motor oil, requiring a change much less frequently.

To enhance the performance and benefits of a lower-priced mineral oil, some oil companies have blended mineral oils with synthetic oils to improve the performance of the mineral oil, attempting to maintain a lower price point than a 100% synthetic lubricant. These synthetic blends are called semi-synthetic motor oil.

Customers, however, need to be aware that there is no standard requiring how much synthetic oil is blended with the mineral oil for it to be called a semi-synthetic engine oil. A synthetic blend oil could be 30% or 5% synthetic–or less. Therefore, the customer needs to weigh the cost-benefit ratio of using a semi-synthetic motor oil compared to using a mineral oil—or a full synthetic oil product.

If you have any questions about conventional and synthetic motor oils, as well as blended oil products and which type of oil products are best for your high mileage vehicles, we’re happy to answer them. We can help you determine what kind of oil will give you the best fuel efficiency, or which is best for vehicles that need to pull heavy loads.

Informed drivers dream of running their engines on real synthetic oil since they know it provides more benefits than conventional oil. If they can’t, they may choose to strike a bargain and opt for semi-synthetic oils which are usually better than conventional oils, but at a lower price point than a full synthetic oil.

What makes synthetic oil so efficient but with a higher price point?

High Precision Purification and Composition

A quality synthetic oil is formulated down to its basic molecules to eliminate impurities. After this, the oil is reformulated with additive packages to fit the dynamic demands of modern day engines.

Each additive that goes into making the synthetic oil is specially designed with a specific purpose:

  • To make the oil resistant to break down hence increasing its lifespan.
  • To make it withstand high temperatures without losing its lubricity and viscosity.
  • To keep it flowing smoothly in cold temperatures, protecting your engine during those cold starts.
  • No impurities means no self-destruction breakdown and sludge accumulation. It may be a good solution for older engines, still in mechanically sound condition, with sludge build up problems due to poor quality oil or maintenance practices.

Semi-Synthetic Oils Mix Conventional Oil to Cut Costs

Synthetic Oil The Best Oil

With so much research and development going into making quality synthetic oil, it can be at a higher price point a customer may not be able to justify. This is where semi-synthetic oil comes in. The hybrid lubricant is a mixture of conventional oil and the high profile synthetic oil at different ratios.

The mix ratio will vary depending on the target price and efficiency. The more the synthetic oil in the blend, the more you will pay per quart and the better the peak performance you should expect. A semi-synthetic blend may have only 5% or 10% synthetic oil since there is no requirement as to what the mixture percentages should be. Therefore, the benefits received may be questionable for the increased price above conventional oils. The buyer should be aware of this fact, and not be misled by unscrupulous marketers.

Which Oil Should You Use?

The rule of the thumb is that you should never downgrade from what your manual recommends. Never run an engine for which a synthetic oil is specified on semi-synthetic or conventional lubricants. This will accelerate wear and tear while reducing engine performance, and may void a warranty.

You can, however, use synthetic base oil on any mechanically sound engine and expect better performance. This will prolong oil and engine life, reduce engine pollution and improve overall engine performance and fuel economy. The result is less cumulative maintenance costs since you will get more miles before major servicing and even get better fuel economy from your engine. A quality synthetic oil may have a higher price per quart, but costs much less to use. The buyer should be sure to not get price and cost mixed up.

At The Best Oil, we offer the highest-quality high performance synthetic oils on the market for the best available prices. Our selection of AMSOIL products are available for factory direct purchasing, giving you extra savings on the highest performing motor oil.


The importance of using good-quality oil in an engine cannot be overstated. AMSOIL synthetic motor oils consistently outperform conventional and other synthetic oils in virtually every category of performance, including wear protection, extreme high- and low-temperature performance, foam control, viscosity retention, rust and corrosion protection, volatility and fuel economy. While other brands may provide good performance in some of these areas, AMSOIL synthetic motor oils consistently perform at the top in every category. Drivers can have confidence knowing that AMSOIL synthetic motor oils provide maximum performance and engine protection.