There is a multitude of ways lubricants can be classified, and for most users out there, it can be overwhelming to understand each classification.
Thankfully, there are substances that can be added to the oil that can, not only minimise wear during boundary lubrication but provide a vast range of additional benefits. Those substances are better known as additives.
Take engine oil for example, what is the difference between 5W-30 and 10W-40? Which one do you pick if you were to buy your engine oil for your next service? With many different brands and ratings such as API, ACEA, ILSAC on the back label, choosing one can be a daunting experience.
First, let us get back to basics: Lubricants are a generic term for a substance that, well, lubricates, meaning to ease the movement between contacting surfaces by minimising friction, heat and wear.
It can come in various forms. The most common is in liquid form we usually call oil. Then we have semi-solid lubricants, better known as grease. Lubricants can also be solid and gas forms. Selecting which lubricant form to use depends very much on the application, the conditions and the constraints.
In this article, we look into the most common form, which is oil, because it in itself can be classified into various types.
Most people would think oil as either mineral or synthetic, but oil types can also be categorised by application, viscosity and performance level.
Oil covers a vast application in the consumer and industrial world. In passenger cars alone, you will have three types: engine oil, gear/transmission oil, and brake/power steering oil although one can dispute that brake/power steering oil is more of a fluid rather than oil.
Go to a large industrial plant, you will see more types: gear oil, hydraulic oil, compressor oil, turbine oil, electrical insulation oil and a couple of others depending on industries.
Those above are examples of lubricant type by application. Each application has its own requirement and using a dedicated oil for the specific application is essential.
Viscosity is another way to classify oil. For engine oil, codes such as SAE 5W-30 or 15W-40 are commonly seen on its label. These are viscosity classifications specific to engine oils issued by SAE International, which is a professional organisation that determines many standards in engineering. The classification corresponds to viscosity levels in two conditions: cold (the characters before the letter “W”) and hot (the characters after the dash “-“).
In the above two conditions, the higher the number, the thicker the oil. So comparing between 5W-30 vs 15W-40 oils, the latter is thicker in both cold and hot conditions because of their higher number. By choosing 15W-40 over 5W-30, you are choosing a thicker oil. There must be a good reason to do so, such as it is recommended in the service manual or you are driving in a hot climate area.
In the next article, we will look into how the oil is categorised via performance level.
About the Author:
Aaron Said is ILD/Sinopec’s National Technical Manager. He is responsible for developing and delivering value-added lubricant technical services to client for reliability improvement, lubricant optimization, and cost-savings. Among his professional credentials are Certified Lubricant Specialist (CLS) and Oil Monitoring Analyst I (OMA) from Society of Tribology & Lubrication Engineers (STLE) and the International Council of Machine Lubrication (ICML)’s Machine Lubricant Analysist I.