Interesting read - synthetic oil

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Synthetic oils have caused countless debates and confusion across nearly every automotive forum, and often with good reason. Legally, the term “synthetic” has a pretty loose definition. While some manufacturers would prefer the word synthetic to only apply to oils chemically formulated without the use of petroleum as a base oil, that is simply not how the rating system works.

The majority of motor oils can be divided up into five different groups. An oil’s group number is dependent on the base oil properties used to derive it. Group I and II oils are created using petroleum base oils, and are considered conventional oil. Group III, IV, and V are considered synthetic, even though group III oils are also derived from a petroleum base oil. Regardless of the derivation, group III through V oils have superior properties and have undergone additional chemical processes which make them differ greatly in quality from groups I & II oils. The group rating alone is not sufficient information to determine if one oil is superior to another; each group has individual advantages and disadvantages.

Speaking more generally of synthetic oils as a whole, versus conventional oils, there are legitimately impressive differences between the two. Consider the creation process of a conventional 5W-30 motor oil. The petroleum base oil alone may have the properties of an SAE 5 grade oil. This means at extremely low temperatures, it may be thick, and at high temperatures, it’s fairly thin. To change this, oil companies incorporate additives into the mix, changing the properties. Pour point depressants can reduce the viscosity at low temperatures, and viscosity index improvers can thicken the oil at high temperatures. The resulting stew of chemicals yields a 5W-30 motor oil, common within the industry. When it’s brand new, a 5W-30 conventional motor oil acts exactly like a 5W-30 synthetic motor oil.

Over time, however, the chemical additives used in the conventional oil to alter its properties begin to break-down, vaporize, or get used up. This means that the oil starts to return back to it’s original base oil, from a 5W-30 back to a straight grade 5 oil for our example. As contaminants begin to work their way into the oil, the overall trend over a long duration is that the oil thickens across the entire spectrum. An old and used conventional 5W-30 oil behave very differently than a brand new 5W-30.

Synthetic oils work quite differently. From the start, the chemical structure is designed to match a specific multi-grade oil. That means even without additives, you could have a 5W-30 motor oil, and then certain additives like rust-inhibitors or dispersants will be added to further improve the usefulness of the oil. The result is that over time the synthetic oil does not degrade away back to a less desirable oil as conventional ones do. From a viscosity standpoint, an old 5W-30 synthetic will act pretty similar to a new 5W-30 synthetic, although likely it will be slightly thicker as a result of contaminants.

Why does all this matter? When engineers design the engine, they’re looking to achieve a certain oil flow rate throughout the system, dependent on the temperature of the engine and the speed at which it’s rotating. As oils age, their flow characteristics change, and this changes how well your engine is protected from wear when it operates outside the boundaries of its initial design. While it’s true that from a viscosity standpoint alone, you could match the protection of a synthetic oil simply by changing your conventional oil regularly, often times synthetic oils come with superior quality additives, leading to a cleaner, smoother running engine as well. There’s a reason why most automotive manufacturers have switched over to synthetics directly from the factory.
Tumelo Maketekete
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Good post thanks.
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That puts it nicely in lay terms. :thumbup:
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Thanks for explaining it in such a way that even I can understand the difference between these oils.
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Thanks Tumelo. Makes way more sense now.

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