Feb 25, 2021 Motul Oils & Lubricants, Taki Bogiages, Motul’s Business Technical Manager, differences between mineral and synthetic oils
Motul Oils & Lubricants: Q&A
We know that oils reduce friction in the engine or transmission while also reducing the amount of heat generated. That’s a given. But with the different products on the market - synthetic, semi-synthetic and mineral-based oils – it’s important to understand the differences, and which is the best choice in each circumstance. As Motul’s Business Technical Manager for Southern and Eastern Africa and the Indian Ocean region, Hippocrates (Taki) Bogiages is the natural choice to talk us through these important questions.
Q: What are the main differences between mineral and synthetic oils?
Mineral oil is refined from a component of crude oil and is the most common and affordable type of lubricating oil in use today. Synthetic oil in contrast is manmade and exceeds the quality and performance of mineral oils in every way. The main differences become apparent at the molecular level, as well as in terms of the purity of the lubricant and the level of contaminates it contains.
Mineral oil is just one of many products that can be refined from crude oil. It generally contains both lubricating molecules and many different contaminates (depending on the extent of refining). These can include nitrogen, sulfur and oxygen, all of which can hinder the oil’s performance.
The properties of synthetic oil are much more predictable. They offer the best parts of a mineral lubricant, without the unwanted compounds that can affect performance
In 1993, the American Petroleum Institute (API) categorised oils into five main groups, based primarily on the method of refining and the base oil properties (Viscosity, Saturates and Sulfur content).
Explanation of the above table:
Group 1
The least refined type of oil which is produced by solvent refining of conventional petroleum base oils. Defined as base stocks containing less than 90% of Saturates, less than or equal to 0.03 percent Sulfur and having a Viscosity Index (VI) greater than or equal to 80 and less than 120.
Group 2
A better grade of petroleum base oil, which may be partially produced by hydrocracking. The clearer colour results from more of the impurities having been removed.
Group 3
The best grade of petroleum base oil, fully refined by processes like hydrocracking, isomerisation, and hydrotreating, which are chemical processes that make these oils purer. Oils in this group may be described as hydro-cracked synthetics. They may be marketed as ‘synthetic technology’.
Group 4
Consists of 100% synthetic oils, man-made, using Poly-alpha-olefins (PAO). Group IV base oils have a Viscosity Index range of 125 - 200. Poly-alpha-olefin (PAO) oils have many benefits, such as oxidative stability at temperature extremes, lower pour points and a generally higher Viscosity Index, which means they can be used in applications with a greater temperature range.
Group 5
A very broad range of base oils, defined as being any type of base oil that does not belong in one of the preceding four groups. Typical Group 5 oils are ester base oils and naphthenic oils. Motul produces certain lubricants that contain group 5 base oil in the form of esters. Motul’s premium 300V range uses EsterCore® Technology, which leads to an increase in vehicle performance and maximises protection of the moving components. We’ll discuss this group in more detail in a future article.
In summary –
Mineral lubricants
Group 1, Group 2
Semi-synthetic lubricants
Blend of Group 2 and Group 3
Mineral-based oil + synthetic oil
Synthetic (mineral-based) lubricants
Manmade lubricants with poly-alpha-olefins
Motul EsterCORE® Technology
A careful selection of a combination of ester base oils
Q: What is the Viscosity Index (VI), and what does it measure?
Viscosity is defined as the measure of a fluid’s resistance to flow: more viscous fluids are more resistant to flow and result in reduced fuel economy and a longer lag in reaching the moving parts of an engine when it is cold started.
In contrast, low viscosity results in a thinner oil film, and therefore, less protection against wear at high temperature.
The Viscometrical properties of a lubricant are often indicated on the can. These tend to reference a specific grading system. The Society of Automotive Engineers (SAE), for example, has established the SAE J300 grading system for engine oils and the SAE J306 grading system for gear oils.
In the case of the SAE J300 grading system, it is important to look at the grades on either side of the ‘W’ (meaning winter). Grades before the ‘W’ indicate the low temperature properties of the multigrade engine lubricant whereas, the grades that follow the ’W’ represent the same lubricant’s properties at optimal engine operating temperature.
The indicated grades range from 0W to 25W (with 0W being the thinnest and 25W being the thickest); these increase in increments of 5W for the cold grade. Higher temperature grades start at 8 and increase in increments of 4 up until they reach 20, whereupon they increase in increments of 10 until 60 (again, the lowest grades are the thinnest and vice versa).
When you refer to the technical data sheet of a lubricant, you will see cSt (centistoke) units used to measure kinematic viscosity. These measurements are taken at 40°C and 100°C, giving two measurements of viscosity for each engine lubricant. This is to enable classification against the SAE grades, which depend on a range of kinematic viscosities. For example, for a lubricant to be classified as an SAE 40 (for engine operating temperature), it must have a kinematic viscosity of between 12.5 cSt and 16.3 cSt at 100°C.
If these conditions are met, the lubricant will be classified as a SAE 40 grade. When we look at the properties at colder temperatures of the multigrade SAE representation, the main focus for this grade is to represent the behaviour of the specific lubricant at engine start up.
Vehicle owner’s manuals contain information on the required viscosity, while the Motul App and website have functionality that return an accurate representation when vehicle details are entered.
When selecting an engine lubricant viscosity, it is vital to ensure that the SAE grade for operating temperature is correct. This will ensure that the oil film in the vehicle at higher temperatures is neither too thick nor too thin for the engine. In turn, this will ensure appropriate protection and oil functioning.
The chosen lubricant should have the same or a lower SAE cold grade viscosity than that specified by the vehicle owner’s manual. This ensures that the properties of the lubricant will deliver maximum protection and better overall engine performance at start up.
Q: What advantages do synthetic oils offer?
As mentioned earlier, synthetic oils contain more stable molecules and fewer contaminants. They are also generally more thermally stable than mineral-based lubricants.
This results in reduced oxidation, making for longer inter-drain intervals and less sludge in the engine (thanks to synthetic oils’ greater resistance to harsh engine conditions). They have improved cleaning properties and are less likely to degrade or vaporise at higher temperatures.
Taken together these factors mean reduced engine wear, reduced oil consumption, and less frequent oil changes.
Q: Are synthetic oils worth the extra money?
When it comes to high-quality synthetic lubricants from reputable and experienced lubricant manufacturers, such as Motul, then yes, they are. The initial cost of purchasing the synthetic lubricant will quickly be offset by the reduction in wear and tear in the engine, the improved fuel economy and the enhanced reliability of the engine or transmission in question. As an added bonus, healthy engines can deliver a performance improvement of up to 3% with a quality synthetic lubricant, as opposed to a mineral oil.
About Taki - Taki holds a BSc in Chemistry and is currently studying for his Honours Degree. He is also a member of the pro Pepson Plastics Kawasaki Motul Racing team. As part of the Know Your Oil powered by Motul campaign, Taki presented online videos highlighting the technical aspects and benefits of using the right Motul products, aimed at the end-user, your customer. These are great to watch as a refresher and to share with your customers to offer valuable info around oils and lubricants. Any questions regarding oils and lubricants, send us an email and we’ll ask Taki to supply feedback in upcoming issues.
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