Synthetic Oil vs Regular Oil: The Definitive GuidePosted by Amsoil, 5th March 2019

In the battle of synthetic oil vs. regular oil, most drivers today know that synthetic oil emerges victorious.

It’s widely understood that synthetic oil provides improved wear protection, engine cleanliness and fuel efficiency, among other benefits. Synthetic oil also lasts longer, offering increased convenience and cost savings.

But what makes synthetic oil better than conventional oil? Let’s find out.

Here’s what we’ll cover:

What is synthetic oil?

How base oils used in regular oils are manufactured

How synthetic base oils are made differently

Is synthetic oil better?

Synthetic oil vs regular oil test

Benefits of synthetic oil

How often should I change synthetic oil?

Synthetic oil vs regular oil change interval

Can you mix regular oil with synthetic oil?

What is synthetic-blend oil?

Fully synthetic oil vs synthetic-blend

Synthetic oil vs conventional oil in older cars

How to switch to synthetic oil

Buy AMSOIL in Australia and New Zealand

What is synthetic oil?

It’s a question driver often pose. They also ask, “What is synthetic oil made of?”

Some erroneously think synthetic oil is not derived from crude-oil sources or other fossil fuels. They think that if all drivers switched to synthetics, we’d sever our ties to fossil fuels and simultaneously save the children, polar bears and whales.

A noble idea, but a false one.

While synthetic and conventional oils differ in performance and how they’re made, they both owe their origins to crude oil or other fossil fuels. But, as you’ll see, they are still vastly different.

Car engine oil, whether conventional or synthetic, is made from two fundamental components:

The base oils are primarily responsible for fighting wear, removing heat and minimizing friction. The addition of different chemical additives to the formulation enhances car engine oil performance. Additives combat chemical breakdown, neutralize acids, provide additional wear protection and more, depending on the formulation and application for which it’s intended.

To illustrate, think of a quart of oil like a glass of lemonade. The base oils are the water and the additives are the lemon concentrate and sugar.

To answer our initial question (What is synthetic oil?), let’s forget the additives for a moment and focus on the base oils.

Buy AMSOIL Online in Australia

How base oils in regular oils are manufactured

The base oils used to make conventional oil are distilled from crude oil.

Crude oil contains hundreds of different hydrocarbons. Oil refineries distil the crude using heat to separate it into different products, including…

Distillation, however, has its limits. Base oils distilled from crude contain several different molecules that are detrimental to lubricating a vehicle’s engine. As a result, oil performance suffers – and so does your engine.

Buy AMSOIL Online in New Zealand

How synthetic base oils are made differently

Synthetic base oils aren’t distilled; instead they’re chemically synthesized (i.e. built).

What does that mean?

Refiners disassemble crude oil molecules to their fundamental components using various chemical reactions. Then, using only uniform molecules (typically ethylene), they build synthetic base oils from the ground up. What results is a pure base oil that doesn’t contain the mishmash of irregular molecules found in conventional base oils distilled from crude oil.

This is all a bit confusing unless you’re a chemist, so let’s use another analogy.

Say you bought an old Victorian house. It’s loaded with character, but it’s seen better days. The foundation is cracked, the plaster is worn, the walls are out-of-plumb and the roof leaks. You decide to make repairs.

There are two ways to go about it: the conventional way and the synthetic way.

The regular way

You fix the foundation, patch the cracked plaster, repair the worn shingles and decide to live with the crooked walls. It’s not a perfect renovation, but it’s economical and the house should provide reliable shelter for a few years before needing more repairs.

The synthetic way

Rather than papering over the glaring problems, you disassemble the house piece by piece. You remove each shingle, piece of siding, nail, brick, stud and joist. Soon, all the house’s components are spread across the yard. Next, you rebuild the house from the ground up using only the straight studs and joists, good bricks, pristine shingles, etc. The final product is far stronger and more robust than the house renovated the “conventional” way.

In the same manner, refiners tear down crude oil molecules into fundamental components and, via organic synthesis, build synthetic base oils using only the molecules that are “straight, square and in excellent condition,” so to speak. The resulting product is optimized for protecting your engine against wear, heat and stress.

(I should point out that this house-building analogy applies to polyalphaolefin [PAO]-based synthetic base oils, and not synthetics made from Group III base oils.)  Not all synthetic oil groups are created equal.

Buy AMSOIL in New Zealand

Is synthetic oil better?

Yes. Thank you, next.

Seriously, though, if you’ve read this far you can arrive at the answer yourself.

Synthetic oil is better than conventional oil.

Synthetic oil is made using pure, uniform chemicals. As such, it imparts benefits conventional oils just can’t touch. It makes perfect sense. Just about anything manufactured with better components is going to provide better performance and last longer – an automotive engine, smartphone, pair of shoes – you name it.

Buy AMSOIL in Your Country

Synthetic oil vs regular oil test

But, don’t take our word for it. The American Automobile Association (AAA) conducted a study to determine if, in fact, synthetic oil outperformed regular oil and was worth the extra up-front price.

Here’s what John Nielsen, AAA’s managing director of Automotive Engineering and Repair, said following the synthetic oil vs. regular oil test:

“Oil protects critical engine components from damage and AAA found that synthetic engine oils performed an average of 47 percent better than regular oils in a variety of industry-standard tests. With its superior resistance to deterioration, AAA’s findings indicate that synthetic oil is particularly beneficial to newer vehicles with turbo-charged engines and for vehicles that frequently drive in stop-and-go traffic, tow heavy loads or operate in extreme hot or cold conditions.”

Those conditions apply to just about any vehicle on the road today.

Our own testing versus conventional oil confirms the AAA’s findings. For example, …

Find the Right Oil for Your Vehicle

Benefits of synthetic oil

We’ve established (and so has the AAA) that synthetic oil outperforms conventional oil. So, what benefits might drivers expect after switching to synthetic oil?

Improved engine protection

Drivers have told us that wear protection is the number-one benefit they demand from car engine oil. If car engine oil could make your car fly, but couldn’t keep components from wearing out and failing, what good would it be?

Synthetic oil does a better job protecting against engine wear. It forms a stronger fluid film to help keep metal components from contacting and wearing against each other. It also offers improved resistance to heat and viscosity loss, two features that translate into better wear protection.

Want proof? Consider the performance of AMSOIL Signature Series Synthetic Motor Oil against a leading synthetic-blend motor oil (more on synthetic-blends later).

Find the Right Oil for Your Vehicle

What about protection in diesel engines?

Again, the evidence shows the superiority of synthetic motor oil in guarding against wear. AMSOIL Signature Series Max-Duty Synthetic Diesel Oil provides 6X more engine protection than required by the Detroit Diesel DD13 Scuffing Test for Specification DFS 93K222 using 5W-30 as worst-case representation.

Buy AMSOIL in Your Country

Improved cold-temperature performance

When the temperature drops, car engine oil thickens and moves slower, causing parts of your engine to remain unprotected for a short period of time. It’s especially problematic with conventional oils since they contain waxes that thicken in the cold. Synthetic oils, on the other hand, don’t contain waxes, meaning they remain more fluid in the cold. This means synthetic oils can reach vital components faster, providing more immediate engine protection and reduced wear. Simply said, synthetic oils offer better cold-weather protection.

See for yourself in the video.


Improved high-temperature protection

Engines get hot. In fact, they run hotter than ever thanks to the proliferation of turbochargers and direct fuel injection, which help car makers achieve today’s strict fuel-economy standards.

Turbos can spin up to 300,000 rpm, while the exhaust gases that drive the turbine can hit 538ºC. The extreme speed combined with the blistering heat can lead to deposit build-up, known as turbo coking, which can ruin the turbo. Turbo coking occurs when oil is left in the turbo and the engine is shut off hot. The heat cooks the oil inside the turbo and leaves behind deposits. 

Look at the image. That glowing chunk of metal is a turbocharger.

It’s up to the motor oil to prevent that from happening. And conventional oils simply aren’t cut out for the task. They contain unstable, light molecules that vaporize when exposed to extreme heat. Synthetic oils, in contrast, offer improved extreme-heat resistance, thus they’re the better choice for today’s hot-running engines. In fact, turbo protection is so important that General Motors requires oils to pass its Turbo Coking Test to be recommended for its GM dexos1® Gen 2 motor oil specification.

We decided to put AMSOIL Signature Series Synthetic Motor Oil to the test. How did it perform? See for yourself. 

Maximum fuel economy

Earlier we talked about how conventional oil thickens when it’s cold. Not only does thick, cold oil affect wear protection, it wastes energy. This, in turn, requires the engine to use more fuel. Because synthetic oils flow readily at start-up, synthetic oils increase fuel economy

In addition, modern low-viscosity oils, like 0W-20, flow more readily than the 10W-40 oils vehicles once used. This, in turn, boosts fuel economy. But formulators must use synthetic base oils to manufacture low-viscosity oils that provide good protection in all areas important to your engine.

Buy AMSOIL in Your Country

Reduced oil consumption

Several factors can cause your engine to increase motor oil consumption. Most are mechanical, including…

If your engine uses oil due to mechanical defects, visit a garage and have them fixed.

However, car engine oil volatility can also contribute to oil consumption. Volatility defines a lubricant’s evaporative loss. The more volatile the lubricant, the higher the tendency to evaporate and exit the engine through the crankcase ventilation system. The more it evaporates, the less oil is left to protect equipment and the more often a user must replace the lost oil.

The small, light molecules in conventional lubricants evaporate at relatively low temperatures. These light molecules require less energy in the form of heat than heavier molecules to be lifted out of the solution and into the air.

Buy AMSOIL in Your Country

Volatility affects more than the rate of oil consumption

When light elements in oil evaporate from heat, the oil’s viscosity increases. This thicker oil forces the engine to work harder, resulting in several problems, including the following:

The solution is to use an oil that’s stable in the presence of heat and resists oil consumption. Synthetic oils offer naturally better resistance to heat and volatility. As a result, they help reduce oil consumption to keep your engine clean and running strong.

For example, AMSOIL Max-Duty Synthetic Diesel Oil provides up to 76% less oil consumption than required by the API CK-4 standard in the Caterpillar-1N oil consumption test.

AMSOIL reduces oil consumption in petrol engines, too, as this graph shows.

Buy AMSOIL in Your Country

How often should I change synthetic oil?

It stands to reason that synthetic oil will last longer than conventional oil due to its superior performance. That’s true, but how long does synthetic oil last?

It depends on the oil itself and your operating conditions.

While synthetic oils in general outperform conventional oil, some synthetic oils are better than others. That means some will last longer than others. Most synthetic oils can last 8,000-10,000 miles. But some synthetic oils today are recommended for drain intervals up to 25,000 miles or one year. AMSOIL Signature Series Synthetic Motor Oil, for example, is guaranteed for 25,000 miles/one year/700 hours, whichever comes first, in normal service. Changing oil once a year reduces waste oil and packaging considerably. Plus, it reduces time and money spent changing oil.

Oil quality helps determine its service life

How long a synthetic oil can last depend on its base oil and additive quality. It also depends on whether your driving conditions fall under the severe or normal designation. Excessive idling; frequent towing, hauling or ploughing; or driving in dusty conditions are examples of severe conditions that can reduce the oil’s drain interval.

We recommend that you follow the oil-change guidelines given in your owner’s manual or on the car engine oil label. Some synthetics are recommended for extended drain intervals beyond what’s given in the owner’s manual. Extending drain intervals in this way allows you to safely change oil less often while spending less on oil over the long haul, if you choose. AMSOIL Signature Series (mentioned above) is one example. Its diesel counterpart, AMSOIL Signature Series Max-Duty Synthetic Diesel Oil, is another. In certain applications, it’s recommended for up to 3X the original equipment manufacturer drain interval, not to exceed 60,000 miles/600 hours of service or one year, whichever comes first.

Used oil analysis is the best method of determining how long your car engine oil can last. It involves taking and submitting an oil sample to a laboratory, where technicians analyse its condition for the presence of wear metals, coolant, fuel and other contaminants. Oil analysis is the most efficient way to determine exactly how long your oil will last and when it needs changing.

Buy AMSOIL in Your Country

Synthetic oil vs regular oil change interval

Remember the 5,000-km oil change? Some quick lubes and shade-tree mechanics may still promote the practice as “cheap insurance” against engine wear. Wanting the best for your engine is a noble idea but throwing out perfectly good motor oil benefits no one (except the company selling you the new oil).

The 5,000-km oil-change interval was adopted and amplified in the 1970s by quick lubes (many of which were owned by oil companies). While they may have had their customers’ best interests in mind, it didn’t hurt that the practice also ensured repeat business.

Those days are over.

Just like vehicles no longer require carburettor adjustments, new ignition points or water in their battery, they don’t require oil changes every 5,000 km (barring extreme operating conditions).

Car engine oil technology has advanced in lockstep with automotive technology, meaning oils today commonly last longer than the traditional 5,000 km. As mentioned above, some synthetic oils offer the ability to extend oil drain intervals if you choose, saving time and money.

Buy AMSOIL in Your Country

Can you mix regular oil with synthetic oil?

Yes, you can mix regular oil with synthetic oil.

There is no danger in mixing the two. Synthetic-blend motor oil, for example, which is readily available at any parts store, is nothing but conventional and synthetic oil already mixed in the bottle.

Mixing the two, however, will only detract from the synthetic oil’s superior performance and reduce its benefits. It’s not a great idea to mix conventional oil and synthetic oil unless you have no choice. If you’re travelling, for example, and notice the engine low on oil, the convenience store alongside the road may only sell conventional oil. In these cases, we recommend draining the oil at your earliest convenience and refilling with synthetic oil.

Car engine oil, whether conventional or synthetic, is made from base oils and additives. While these components are compatible with each other, the base oils in synthetic oils are higher quality. The additives, too, are often higher quality. At the end of the day, it’s safe to mix them, but why bother when you’re simply diluting the high-quality synthetic oil?

Buy AMSOIL in Your Country

What is synthetic-blend oil?

We alluded to the answer above: it’s nothing more than car engine oil that’s formulated using both conventional and synthetic base oils. Synthetic-blend oil is also referred to as semi-synthetic.

Synthetic-blend oils fall in between conventional oil and synthetic oil on the car engine oil spectrum. The idea behind them is to offer drivers a taste of the improved performance of a fully synthetic oil at a price closer to a conventional oil. Oil marketers see them as a stepping-stone product to help encourage motorists to eventually step up to a full synthetic.

The biggest question surrounding synthetic-blend motor oil is, “How much ‘synthetic’ is in my oil?” Does the oil in the bottle include 1 percent synthetic base oils? Ten percent? Thirty?

The higher the synthetic content, the better the oil should perform.

Buy AMSOIL in Your Country

Fully synthetic oil vs synthetic-blend

Unfortunately for drivers, there are no industry specifications or regulations that define the minimum percentage of synthetic components for a synthetic-blend to be classified as such. It varies depending on each manufacturer, and they’re not going to divulge that information since it would give their competition an advantage.

That being the case, astute drivers can look for a few clues to help interpret the amount and quality of the synthetic base oils in your synthetic-blend oil.

Visit the oil manufacturer’s website and find the oil’s technical data sheet (also called a “product data sheet”). Find the section labelled “Typical Technical Properties,” or some derivative of such. Look for these two values:

You should know, however, that an oil’s base oil composition is only part of what determines its performance. The additives also play a large role in fighting wear and deposits.

Synthetic oil vs regular oil in older cars

Misinformation about synthetic oil vs conventional oil in older cars still populates the Internet and some auto repair shops. Some people still erroneously think that synthetic oil can be “too slippery” and result in leaking seals. Or synthetic oils will cause roller followers to slip or skid.

Like many popular misconceptions, the idea that synthetics cause oil leaks is based on truth.

Back in the 1970s, some synthetic oils were formulated using chemicals that were harder on seals than the chemicals in modern synthetics. Early formulations sometimes resulted in oil leaks, which gave rise to the myth that exists today. Modern synthetics, however, are much more advanced and use chemicals that are fully compatible with seals. A properly formulated synthetic conditions seals and helps maximize their life and effectiveness.

Synthetic oils can reveal the true condition of seals

Sometimes, switching to a synthetic oil in an older, high-mileage car can result in leaking seals, but it’s not the motor oil’s fault.

The seals and gaskets in older engines can dry, become brittle and crack. Sludge that has accumulated over the years, however, can cover the cracks and prevent them from leaking. It’s like using spackle to cover cracks on a wall. The sludge effectively helps the worn seals do their job.

A good synthetic uses potent detergent additives that clean sludge, revealing the true condition of the seals. Cleaning the sludge from the worn seals leads to leaks, which the driver associates with the synthetic oil.

If you suspect your older, high-mileage engine falls into this category, you may want to leave well enough alone and continue using conventional oil.

How to switch to synthetic oil

Given its superior performance, many motorists are making the switch to synthetic motor oil for the first time. Several automakers install synthetic lubricants at the factory due to their improved protection, which further encourages motorists to use synthetic motor oil.

If you decide to opt for a full synthetic oil change next time your vehicle is due, here’s what you need to do first: nothing.

That’s right. You need not do anything special to switch to synthetic oil. Simply drain the conventional motor oil and install synthetic motor oil of the correct viscosity for your engine.

Consider an engine flush

Depending on the condition of your engine, you may want to perform an engine flush to remove sludge prior to switching to synthetic oil.

Synthetic oil beats regular oil

Synthetic oil outperforms regular oil on nearly all counts. It delivers excellent protection against wear, damaging deposits and chemical breakdown. Switch to synthetic oil to help your engine last longer and deliver maximum power and performance.

Where to buy AMSOIL

Back to blog

Next post

About cookies on our website

We use cookies to give you the best experience on our site. By continuing to browse, you are agreeing to their use. Read more...