Synthetic Vs. Conventional Oil
What’s The Difference?
Motor oils are divided into five major groups. Groups 1 and 2 are what we call “conventional oil,” and are created using petroleum base oils. Groups 3, 4, and 5 are chemically formulated synthetic oils, even though group 3 oils are derived from a petroleum base. Regardless of the derivation, synthetic oils are engineered to have superior qualities compared to the group 1 and group 2 conventional oils. From this point forward, we will strictly refer to groups 1 and 2 combined as conventional, and groups 3, 4, and 5 as synthetic.
To understand the performance differences between conventional and synthetic oils, we must look at how they are made. The oil we use in our cars today is multigrade oil, which must meet viscosity requirements at two temperatures in order to be suitable for year-round use. Conventional oil starts off with the properties of a monograde oil. To illustrate this, we will use conventional 5w30 oil as an example. The petroleum base oil alone has the properties of an SAE 5 grade oil. This means, at low temperatures it is thick (viscous), while at high temperatures it is very thin. To ensure that the petroleum base oil can sufficiently protect the engine at high temperatures, oil companies use additives to make the petroleum base SAE 5 grade oil into a multigrade 5w30 oil. Pour point depressants are used to reduce the viscosity at low temperatures and viscosity index improvers can thicken the oil at high temperatures, thus producing 5w30! When brand new, conventional oil and synthetic oil behave exactly the same.
However, over time the chemical additives used in the conventional oil to change its properties begin to break down. As these additives start breaking down, the conventional 5w30 from our example starts to return to its original straight grade 5 base oil. As this happens, the oil thickens, causing used conventional oil to behave very differently from new conventional and synthetic oil. As you can see below, the used conventional oil on the left is much thicker and does not flow at the same rate as the new conventional oil, or the new or used synthetic oil.
Synthetic oil is much more stable. From its beginning, its chemical structure is designed to match a multigrade oil without the incorporation of any additives– its base is a true multigrade oil! Some additives are added to synthetic oils to further improve their usefulness, such as rust inhibitors and dispersants, but they are not required to achieve the required viscosity at “winter” and “summer” temperatures. As a result, synthetic oil does not degrade back to a straight grade oil. This means that the viscosity of used synthetic oil behaves very similarly to new synthetic oil, though it may be a little thicker as the result of contaminants.
Why Does It Matter?
When engineers design the engine for your vehicle, they require a certain oil flow rate depending on variables such as temperature and rotating speed of the engine to ensure the moving parts are properly lubricated. As conventional oils age and their flow characteristics change, the engine may not receive the protection it needs, thus causing massive amounts of wear and tear that can drastically shorten the life of your engine.
From a viscosity standpoint, you can achieve the same protection as synthetic oil with conventional oil through frequent oil changes. However, synthetic oils often include superior additives that lead to a cleaner and smoother running engine.