The differences between mineral, synthetic and synthetic-based engine oil
Did you know that classic and older generation cars primarily use mineral oil? Or, that there are very sensible reasons to make a switch from synthetic to synthetic-based oils?
Choosing the type and the viscous gradation of engine oil can be quite confusing to an ordinary user. This is why it’s usually something we leave to our mechanic or salesperson to decide for us. This article, written by our expert associate Dr. Stevan Dimitrijevic, aims to clarify the differences between mineral, synthetic and synthetic-based oil, which is primarily conditioned by their purpose.
Mineral Engine Oils
It is common for mineral engine oils to be made out of conventional mineral base oils which are created via distillation and crude oil and additive refinement. Mineral base oils (API group I) have a low viscosity index (around 100) and are highly vaporable when it comes to low viscosity base oils. That is why they don’t come in handy when making SAE 0W-xx and 5W-xx.
API group II are base oils which are treated by hydrogen in order to remove i.e. convert all unsaturated hydrocarbons (CH) into saturated ones.
Mineral engine oils are less resistant to high temperatures and oxidation compared to synthetic engine oils, which is why they have to be changed more often, after every 5.000 to 10.000 kilometers, depending on the additive package, the engine type and the exploitation conditions. They have higher liquid points, which makes them favorable for winter conditions and extremely low temperatures, usually used at up to - 15 °C (SAE 15W-40).
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Synthetic Engine Oils
Synthetic engine oils are the kinds of oils which are made out of synthetic base oils and additives. They belong to API groups III, IV and V.
API group III are base oils which are made through the process of hydrocracking (molecule conversion), and which meet heavy standard demands for base group III. Their characteristics are similar to the characteristics of base oils from groups IV and V, but their price is lower. Base oils from groups IV and V are made by means of various synthetic processes.
Owing to a different composition and characteristics, synthetic engine oils have better characteristics than mineral engine oils – practically all those that are relevant if we consider standards and approvals. The superiority of synthetic engine oils is such that it cannot be made up for even by a more frequent mineral oil change, in which case the cost is not only equal to that of frequent mineral oil change, but goes in favor of synthetic oils.
Synthetic engine oils handle high temperatures better and they are more liquid at low temperatures. Due to their better thermic and oxidative stability/resistance, synthetic engine oils last longer, which is why their change intervals are 2 to 3 times longer. They provide better engine protection, especially from wear and corrosion, and they also contribute to engine cleanliness, seeing it as they create practically no residue.
Synthetic engine oils provide a lower level of exhaust emission, which makes meeting the new Euro standards, especially V and VI, possible. Furthermore, this engine oil category enables meeting the newest standards’ heavy demands, ACEA and API, as well as the latest manufacturers’ approval demands, which mineral engine oils cannot achieve. Synthetic engine oils of low viscosity (0/5W – 20/30) reduce internal resistance, thus increasing engine power and torque, and reducing fuel consumption.
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The only thing that goes in favor of mineral oils is that they come at a lower price than synthetic oils.
There is a lack of some viscosity grades for older vehicle models, but in that case, if the engine is in good condition, alternative viscosity grades become a possible option. A higher level of engine oil quality can only be a plus, seeing it as new standards cover old ones.
Synthetic-based Engine Oils
As we stated in the introductory part, synthetic-based engine oils are made out of a combination of mineral and synthetic base oils, with the right additives. The composition of additives is identical or similar to mineral engine oils, which is why synthetic-based engine oils are, as far as their quality is concerned, closer to mineral engine oils. The concentration of synthetic base oils in the final product is 20 to 30 percent (25 to 40 percent of the base), which makes them, by composition, more similar to mineral engine oils.
Synthetic-based engine oils used to be an optimal choice for most vehicles in the 1990-s. Nowadays, they are, however, simply a cheaper alternative for vehicles with high mileage, as well as a mineral oil “extension” in a sense that the addition of a synthetic component makes viscosity grades, such as 10W-40 and 15W-50, or even 5W-40, possible.
This engine oil category is not strictly defined, which is why the intake of the synthetic component, in the case of (very) cheap synthetic-based engine oils, is lower, and sometimes even base group II oils are used as the synthetic component. This contributes to a lower price, but also to a lower level of quality. It is also the reason why it is recommendable to purchase this engine oil category from eminent manufacturers, especially the premium brand category.
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Synthetic Technology Engine Oils
A special engine oil category is consisted of so-called synthetic technology oils which are made out of HC oils that belong to base group III (according to API). These are not completely synthetic oils, but the additives are completely identical or similar to those in synthetic engine oils.
This engine oil category is especially common among freight vehicles or motorcycles. Synthetic technology engine oils are characterized by a very good price-quality ratio.
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NOTE ON MIXING ENGINE OILS
Mineral and synthetic engine oils can be mixed, but this needs to be avoided, except in emergencies, such as, for example, when you need to finish your driving and the right engine oil category is not available. By mixing mineral and synthetic engine oil you will not get synthetic-based engine oil, at least not a good one. What’s more is that by acting so you will not improve the quality of the mineral engine oil, and you will drastically reduce the quality of the synthetic engine oil, even with a small amount of the mineral one.