Oil specifications - ACEA vs APIĪpart from the viscosity index, there are other factors to consider when choosing an engine oil for your vehicle. For example, a 75W90 transmission oil doesn't have a higher viscosity than a 15W40. If you are interested, you can see more information regarding SAE specifications here.īut be careful: transmission oils have a different SAE numbers. Here you can see the recommended oil for each ambient temperature: You should be aware of climate changes in order to keep your engine fully functional. The number before the W represents the oil viscosity at lower temperatures, while the second number (after the W) indicates the viscosity at operating temperatures.įor example, this means that 5W30 engine oil has less viscosity at lower and higher temperatures when compared to 10W40. The SAE (Society of Automotive Engineers) established a numerical code to represent the viscosity of oil at both hot and cold temperatures. Some synthetic oils are able to achieve this variation without additives. To be able to change the viscosity index, conventional oils incorporate additives, usually plastic polymers. Thus, the viscosity index measures the ability of an engine oil to resist becoming thinner at high temperatures. The viscosity changes with temperature to ensure protection and operability under all circumstances. A higher viscosity implies a slower flow and a thicker fluid. Viscosity is simply the resistance of a fluid to flow. 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.After a brief review of the use of engine oil, we will now move on to one of the most important concepts: oil viscosity index. He is responsible for developing and delivering value-added lubricant technical services to client for reliability improvement, lubricant optimisation, and cost-savings. Want to know if the viscosity index of your oils are suitable for your operating conditions? Our technical team can assist!Īaron Said is ILD/Sinopec’s National Technical Manager. VI also can be increased by adding a VI improver additive, which is basically a polymer that contracts or expands depending on temperatures. Lubricants with high VIs are typically synthetics or hydrocracked mineral base oils that sit on the higher side of API grouping such as Group III. Oil A should be selected for higher temperatures or applications where the gaps between low and high temperatures are large. For machines that operate under low to moderate temperature, Oil B may be suitable. Oil A has a wider temperature range as it will still be within the range until slightly beyond 100⁰C. Oil B meets the optimum viscosity range up until 60⁰C after which it will be too thin. To illustrate this, consider the same Figure 1 chart with the optimum viscosity range added (see Figure 2). Specifying the VI will ensure that variations in temperature will have no, or little impact, as the viscosity will still remain within optimum range. However, changes in temperature may put the lubricant viscosity out of the range: either too thick or too thin, for the machine to operate reliably. Each machine is designed to run with an optimum viscosity range to ensure sufficient film thickness. The knowledge of VI helps in lubrication selection. In other words, the higher the VI, the wider the operating temperature the oil can operate without losing its protection abilities. Consider Figure 1 below: even though Oil A and Oil B have similar viscosity at 40⁰C, due to Oil A having a higher VI, its viscosity at 100⁰C decreased a lot lesser then that of Oil B. Two lubricants may have the same viscosity at 40⁰C, but will not be at 100⁰C if their VI is different. The rate of which it increase and decrease is what VI is about. The viscosity will reduce as a lubricant heats and then increase when it cools down. It is a way to describe a lubricant’s viscosity variation, or sensitivity, to changes in temperature. Viscosity Index or VI is the viscosity behaviour in differing conditions. This is especially true for machines that operate under wide temperature ranges. We need to know how the viscosity changes with temperature. However, knowing the right viscosity for the application is not enough. As mentioned in the previous article, viscosity is a very important property of lubricant.
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