Engine Oil Grades Explained

Learning engine oil grades is pretty much the same as learning the basics of any machine we frequently use. For example, we all have been in a situation where we had to call a mechanic as an electric appliance at home faced some technical issue. In such times, when the mechanic tells us about the fault, we wish we knew more or at least the basics of that electric appliance so that we can understand the fault better or avoid being duped. Even if the mechanic is not trying to dupe us, having basic knowledge always brings a sense of confidence.

In the same way, when a mechanic suggests or asks you as to which grade of engine oil should he top up your car’s engine with, you feel more confident if you know what engine oil grades are. In this article, we explain the various engine oil grades and their vocabulary to help you make an informed decision while choosing the right engine oil for your car.

What are Engine Oil Grades?

Before learning about engine oil grades you need to know what viscosity is. Viscosity is a property of liquid and it means resistance to flow, or simply how thick the liquid is. The lower the viscosity the faster the fluid flows. SAE (Society of Automotive Engineers) which is a global standards organisation grades engine oils according to their viscosities to classify them.

How to Read Engine Oil Grade?

The engine oil grade is written in an alpha-numeric code, for example, 15W – 40. Let us understand what each character of this alpha-numeric code means.

• The W stands for WINTER, and the number before W, 15, represents the oil’s viscosity at low temperatures or when the engine is cold. The lower an oil’s viscosity the better its ability to be pumped and flow at colder temperatures. Therefore, in extreme cold conditions and at engine start-up, as compared to 5W oil, 0W oil will be able to flow faster and reach key engine components such as pistons, valves, cylinder walls, and others.
• The number after the hyphen (-), which in this case is 40, represents the viscosity of the oil at normal operating temperatures, which in an engine is around 100 degrees Celsius.
• The wider the gap between the viscosities of an oil at lower and higher temperatures, the better its capacity to cope with temperature variations. At the same time, the viscosity of the engine oil cannot be too thin or too thick. An engine oil that is too thin will not be able to make a protective layer around engine parts, causing higher wear and tear. An engine oil that is too thick will put a higher load on the engine as it will work against the agility of moving engine parts.

A good way to learn how oil behaves at different temperatures is to observe the cooking oil when you pour it into the frying pan. When you do not fire up the stove, the oil is at its thickest form, and as the pan heats up it gets thinner and runnier.

Engine Oil Grades

Here are some globally used engine oil grades.

0W – 20

Since the viscosity of this oil is zero in cold conditions, it is the thinnest before you start the engine. When the engine reaches its normal operating temperature the oil’s viscosity increases to twenty, making it slightly thicker.

0W – 30

Same as the first one, the viscosity of this oil is zero at cold conditions and it tends to get relatively thicker at normal operating temperature as its viscosity reaches thirty.

0W – 40

Much like the previous oils on this list, this oil is thinnest before the engine starts and gets thicker at normal operating temperature as its viscosity reaches forty.

5W – 30

For the Indian conditions, this is an optimum range of viscosity – neither too low at low temperatures nor too high at higher temperatures. This is why it is the most extensively used and widely recommended engine oil in the Indian market.

5W – 40

This fully synthetic engine is slightly viscous before the engine starts and it gets substantially more viscous when the engine reaches normal operating temperature.

10W – 40

This engine oil is the most viscous one at low temperatures and it gets substantially more viscous when the engine reaches normal operating temperature.

Types of Engine Oils

An engine oil is not a single oil, rather it is a mixture which consists of a base oil and some additives. It is done to develop the types of engine oils according to the types of engines and driving conditions. This is why the engine and driving conditions are two crucial factors in determining the right engine oil for your car. Based on the viscosity, effectiveness, and efficiency, engine oils can broadly be categorised into a few types.

Conventional or Mineral Oils

These are the crudest engine oils and are produced by refining petroleum oils. With some additives homogenised with them, these types of engine oils undergo specific treatment to improve their performance and work fine under a wide range of temperatures. At the same time, mineral oils are cheaper and used mainly in older vehicles and motorcycles.

The SAE ratings for these oils are such as 10W – 30 or 20W – 50. As can be seen, the viscosity of mineral oils is on the higher side at lower temperatures as they deliver negligible lubrication in cold start conditions. Moreover, mineral oils are seriously ineffective in protecting engine components against friction-induced heat and make them prone to break-down at higher temperatures. These mineral oils need to be replaced more frequently as compared to the other types of engine oils and they do not last more than 5,000 km.

Semi-synthetic Engine Oils

As the name suggests, a semi-synthetic oil is a blend of a small volume of synthetic oil mixed with a mineral oil. Therefore, these oils strike a balance between the affordability of mineral oils and the effectiveness of fully synthetic oils. These oils are also known as synthetic blend oils. Meanwhile, semi-synthetic oils are nearly thrice as effective as the mineral oils. Adding some volumes of synthetic oil with mineral oil enhances its viscosity and functionality under a wider range of temperatures and stress.

Some synthetic blend oils are also formulated for older vehicles that have been driven more than 1 lakh kilometres. Such high-mileage vehicles are relatively more susceptible to cracked seals, oil leaks and/or oil burn-off. To cope with such problems, some special synthetic blend oils which are also known as high mileage oils, come with some special additives to offer extra protection and they are usually labelled with ‘High Mileage’ or HM.

Fully synthetic Engine Oils

Synthetic oils are the most advanced engine oils and are developed by breaking down the mineral oils into their rudimentary molecular forms. Due to this, it becomes easy to remove all impurities from the oils, making the molecules of the engine oils consistent in terms of size and shape. Synthetic oils offer next-level lubrication as compared to their counterparts. They function supremely in both high and low temperatures, and under severe stress. Since the technology and the effort that goes into making synthetic oils are expensive, they are costlier than other types of engine oils.

Terminology related to Engine Oils

On the labels of the engine oils, some terms and abbreviations are mentioned which can be confusing if you do not know their meanings. Here are some commonly used terminologies on engine oil labels.

SAE Viscosity Rating

SAE rating is a measure of the viscosity of oil and high and low temperatures. For example, a rating that reads “0W-30” indicates that the viscosity of the oil remains zero at low temperatures and reaches forty at high temperatures/ normal operating temperatures.

API Service Classification

American Petroleum Institute (API) is a USA-based trade association for oil which certifies the oils. The API symbols mentioned on a label indicate the suitability of the engine oil for a petrol or diesel engine. To categorise oils, they use S is for ‘Spark Ignition’ which is for petrol engines and C is for ‘Compression Ignition’ which is for diesel engines. In both types of symbols, the letter S or C is followed by another letter. For example, SM or CF. The higher the second letter, the more advanced the oil.

ILSAC Rating

Founded in 1992, the International Lubricant Standardization and Approval Committee (ILSAC) is a global organisation in which Ford, General Motors, Chrysler and the Japan Automobile Manufacturers Association (JAMA) develop minimum effectiveness and efficiency standards for engine oils used in petrol-powered cars. ILSAC oil ratings are founded by API categories with additional more stringent tests which include a chain wear test and a test for fuel economy fluids. Moreover, there is a specific test to protect against low-speed pre-ignition (LSPI) which occurs in some petrol engines. The ILSAC rating is mentioned in the letters “ILSAC GF-x” on the label, where “x” represents the performance and recency level, for example, ILSAC GF-6 is a more recent one than ILSAC GF-5. 

OEM Approvals

OEM or Original Equipment Manufacturer approvals indicate that the specific manufacturer has approved the oil for use in their engines. For example, the label – “Mercedes-Benz Approved” means the oil is suitable for Mercedes-Benz engines.

Summary

Engine oil is as essential for an engine as water is to us. Not only does it lubricate engine components, but also cleans them and protects them from corrosion. However, you cannot just pour any random engine oil into your car’s engine and jeopardise the life of your car’s heart. Every engine requires a specific type of engine oils and engine oil grades are where the categorisation of the engine oils starts. This article explains the engine oil grades along with some classifications of engine oils and some commonly used terminologies related to engine oils.

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