If, like me, you always wondered what does 5W30 or 25W50 mean? Well, we will discuss it further in detail below.

The lifeblood of the internal combustion engine, motor oil, is vital to the performance of your vehicle. With many moving parts, your engine builds up friction and heat as all these parts rub together. Motor oil not only lubricates the engine, it also absorbs heat to help it run smoothly and efficiently.

So, in detail, what does motor oil do exactly?

1.Provides Lubrication

• The motor oil lessens the friction amongst the various components of the engine during the combustion cycle. By providing a thin layer of oil, parts of the engine do not rub each other harshly. Thus engine oil reduces the wear and tear.

2. Neutralizes Acids

During the process of combustion, fuel and as well as the oxidization of other lubricants produce acids. Engine oil is responsible for neutralising these acids.

3. Cleans out Sludge

Engine oil plays an important role in making sure the engine block is clean and free from residue. If the engine sludge is not properly removed, this could lead to blockage.

4. Inhibits corrosion and oxidation

Another function of engine oil is preventing corrosion. Motor oil protects the cylinder blocks from rust.

Types of motor oil

Conventional oil – The industry standard for many decades, conventional oil is made from crude oil that has been pulled from the ground. The oil is refined and combined with additives that help with engine protection, viscosity and heat breakdown. The least expensive kind of motor oil, you can expect to change it between 5,000 and 7,500 kilometers.

Synthetic oil – Made up of chemical compounds, synthetic oil is created in the lab. High-performance additives are blended in to enhance friction-reducing properties. Synthetic oil is effective at reducing friction, handling extreme temperatures and flowing well through the engine. Designed to be changed between 15,000 and 30,000 kilometers, synthetic oil can last up to three times longer than conventional oil. While it is typically the most expensive oil, you could end up saving money thanks to fewer oil changes.

Synthetic blend oil – A hybrid of conventional oil and synthetic oil, synthetic blend oil gives you many of the benefits of full synthetic oil without the higher cost. The chemical additives help resist oxidation and improve performance in extreme temperatures. On average, you can expect to go about 15 000 kilometer between oil changes.

High mileage oil – Designed for vehicles with more than 100,000 kilometers on the odometer, high mileage oil has additives and seal conditioners that can help reduce leaks and extend engine life. High mileage oil can also protect against deposit buildups, sludge and friction. Manufactured in different formulations including conventional, synthetic and synthetic blend, be sure to read the label to know what kind of high mileage oil you are getting.

Now to the crux of the matter!

Each engine oil label includes its grade. If you look at the label, you’ll notice some numbers and letters that make sense only to those who know how to interpret this combination. The rationale behind this system is very simple. Namely, with the development of science and technology, we’ve been introduced to a wide range of engine oil grades.

Each oil has been designed to provide maximal performance in specific operating conditions. Still, you probably don’t know what those numbers and letters mean. So, let’s try to make sense of this ‘code’.

The Society of Automotive Engineers (SAE) (So that is what it stands for:) ) defines a numerical system for grading motor oils according to viscosity.

Oil Viscosity

The first piece of information speaks to viscosity grade. Viscosity is simply the resistance of a fluid to flow. A higher viscosity implies a slower flow and a thicker fluid. The viscosity changes with temperature to ensure protection and operability under all circumstances. Thus, the viscosity index measures the ability of an engine oil to resist becoming thinner at high temperatures. conventional oils incorporate additives to change its viscosity. 

To fully understand the different grades of motor oil, you need to know what the numbers and letters mean. Let’s look at 10W-40 oil.

If you want to learn to interpret what the different labels stand for, you should know what the numbers and letters mean. To help you understand, we’ll take a look at 10W-40 oil, for example. The letter “W”, believe it or not, stands for winter. The first number, in our example: 10W, refers to the cold weather viscosity (flow rate) of the oil, i.e. it shows you how viscous the oil is before the engine reaches its normal operating temperature. In case you don’t remember your physics classes, viscosity represents the level of internal friction of the fluid.

Since we know that lower friction enables better flow, it’s easy to understand that a 10W oil will flow better in cold temperatures than its counterpart with a higher number. Also, we need to go back to our physics lessons one more time and remember that oil thickens at low temperatures. That’s why drivers living and driving in a cold climate should opt for oil with a lower number before ‘W’.

Now that we understand what the first number represents, it’s time to focus on the second one, which is 40 in our example. It shows how thick the oil is under normal operating temperatures. Logically, a higher number means that the oil is thicker and also less prone to thinning at higher temperatures. That’s why grades like 15W-40 and 20W-50, for example, were developed for use in warm climates, since the first number (before ‘W’) is relatively high in comparison to oils with ‘0’ or ‘5’, for example, which are more suitable for colder regions.

Motor Oil Grades

Take a look at some internationally used engine oil grades-

1. 0W-20 This engine oil is relatively thinner when you start the engine. Here in 0W-20, the viscosity of the oil is 0 when the motor is cold. When the engine reaches its normal operating temperature the viscosity of the oil becomes 20.
2. 0W-30 The 0W-30 oil is engineered to behave as a 0 weight oil at the starting temperature and a 30 weight oil when the engine reaches its normal operating temperature.
3. 0W-40 The 0W-40 oil is engineered to behave as a 0 weight oil at the starting temperature and a 40 weight oil when the engine will reach its normal operating temperature.
4. 5W-30 5W-30 is the most commonly available and most extensively used engine oil in the Indian market. Most of the Indian car manufacturers recommend this.
5. 5W-40 5W-40 is the fully synthetic engine oil which performs like a 5 weight engine oil when experiencing a cold start. It acts like a 40 weight oil once the engine reaches normal operating temperature.
6. 10W-40 10W-40 is the engine oil which offers a 10 weight performance in the cold starting temperature. On the other hand, it provides a 40 weight performance at the normal operating temperature of the engine.

NOTE: Ambient temperature in ºC

Motor oil is indispensable to your car engine. It makes sure that the motor works in the best condition possible. So which engine oil should you go for? This would depend on the car you drive as well as where you drive it. However, remember to choose the manufacturer specified engine oil for your car.

Also, look out for your car and get the oil changed periodically. Wondering who the best person is to buy oil for your car? Think Tjör Motor Spares Centre. We are here to assist you!

Stay tuned for our next blogpost!

Happy reading!

List of References

Champions Auto Parts, https://www.championautoparts.com/Parts-Matter/by-the-numbers/All-About-Motor-Oil.html, accessed 13 January 2024, 

Valvoline, https://www.valvolineglobal.com/en-eur/understanding-car-engine-oil-grades/, accessed 13 January 2024,

Go Mechanic, https://gomechanic.in/blog/car-engine-oil-grades-explained/, accessed 13 January 2024,

Total Energies, https://lubricants.totalenergies.com/consumers/maintenancetips/Oil-viscosity-and-oil-grades, accessed 13 January 2024