Synthetic Oil vs. Conventional Oil: The Definitive Guide

Here’s what we’ll cover:

What Is Synthetic Oil?

It’s a question drivers 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:

• Base oils
• Additives

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.

How Conventional Base Oils Are Manufactured

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.

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.

Synthetic Oil Vs Conventional 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 conventional 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. conventional oil test:
“Oil protects critical engine components from damage and AAA found that synthetic engine oils performed an average of 47 percent better than conventional 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, …

• AMSOIL Signature Series 5W-30 showed 53% less oil consumption than conventional motor oil, requiring less-frequent top-offs vs a national conventional brand 5W-30 in the ASTM D5800 NOACK volatility test

• AMSOIL synthetic motor oils make cold weather starting 39% easier than conventional motor oils, based on testing of AMSOIL Signature Series 5W-30 against a national conventional brand 5W-30 in the ASTM D5293

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 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

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 improve fuel consumption. 

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.

Reduced Oil Consumption

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

• Leaking seals or gaskets
• Stuck or worn piston rings
• Worn or damaged bearings
• Clogged PCV valve

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.

Volatility Affects More Than The Rate Of Oil Consumption

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.

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

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.

Synthetic Oil Vs Conventional Oil Change Interval

Can You Mix Conventional Oil with Synthetic Oil?

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.

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:

• Viscosity Index: Oils with a higher number include a better synthetic base oil that provides more protection to critical components over a wide temperature range by maintaining fluid thickness and the necessary fluid barrier between parts.
• Pour Point: measures the oil’s fluidity at cold temperatures and refers to the lowest temperature at which oil maintains its ability to flow. Lower numbers are likely to indicate a better synthetic base oil.

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 Conventional Oil in Older Cars

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 Conventional Oil

Synthetic oil outperforms conventional 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.