I am hoping that most of you are aware of the different terminologies associated with engine oils. Feel free to breathe a sigh of relief as I am not talking about the umpteen brands available in the market, but the grades of engine oil used in different cars during different seasons and occasions. A question which I am asked often is – What differentiates these grades of oils and how does it affect the functioning of a given engine?

Oil in any machine has the primary purpose of lubrication; it creates a thin, viscous layer between the metal surfaces, stopping them from grinding against each other thus, reducing wear and tear. Every engine manufacturer recommends a certain grade for oil for its engine’s optimal performance. Allow me to list the various grades on offer.

Composition of Engine Oils

Engine oil generally consists of 80 percent of base oil and 20 percent performance additives. The additives include anti-wear additives, antioxidants, dispersants and detergents that keep the engine clean. The viscosity index enhancers ensure that the liquid maintains viscous nature of the oil throughout the engine’s operating temperature range. The base oil is responsible for carrying these performance additives to where it is needed, drawing heat away and providing vital cooling to the engine components. The base oil specified consists entirely of either mineral oil or synthetically manufactured oil or the mixture of the two, which is often known as part-synthetic or semi-synthetic engine oils.

Advantages of Different Types of Oil

Fully-synthetic engine oils are specifically engineered to meet specific demands, which generally help engines derive heightened performance, improve protection and higher fuel economy. It is also observed that these modified fluids remain highly stable at high temperatures and viscous enough when it is extremely cold. Synthetic oils though provide the best results, are on the expensive side. Thus, the mass market carmakers generally do not recommend the same to keep the service costs low.  

Semi-synthetic ones are a mixture of mineral and synthetic oils. Their composition is evenly balanced to provide better performance, protection and fuel efficiency as compared to mineral oils. On the other hand, mineral oils are naturally occurring crude oil, refined and processed to remove waxes and impurities.

The reason why synthetic engine oils perform better can be attributed to its molecular structure. Mineral oils consist mainly of molecules of different shapes and sizes. In contrast, synthetic oils are carefully made in a controlled process and engineered to meet more specific requirements. The results derived from synthetic are improved lubrication in varied weather conditions, increased engine performance, better fuel efficiency, enhanced cleanliness and engine life.

Deciphering The Nomenclature

Engine oils are rated viscosity of the liquid. And viscosity is the fluid’s resistance to flow. Denoted by XW-WW, the preceding the “W” rates the oil’s flow at -17.8 degree Celsius. The lesser the number, the less it thickens in the cold. So, oil rated at 5W-30 thickens less than a 10W-30. A car primarily destined to run in extremely low temperatures would benefit from 0W or 5W rated engine oils.

The number denoted after “W” rates the fluid’s viscosity at 100 degree Celsius and measures the oil’s resistance to thinning at higher temperatures. Say, 10W-30 will thin out at higher temperatures faster than 10W-40.

All carmakers recommend a grade of oil to be used in a specific model. It’s advisable to stick to the recommended grade as long as you religiously stick to the prescribed service schedule. Try not to switch between engine oil grades, say from synthetic to semi-synthetic. Until there are performance upgrades that require certain high-grade oils, try to stick to your recommended grade of oil for stable performance, efficiency and engine longevity.