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Let's start with understanding viscosity. Your owner's manual may tell you to use SAE 5W-30 engine oil. What does this mean? SAE stands for the Society of Automotive Engineers. They have created a standard for identifying the viscosity characteristics of engine oil. The 5W-30 part of the symbol is actually just a name. The W part of the name is an indicator of low temperature viscosity properties while the 30 part of the name is an indicator of the high temperature or operating viscosity properties. The numbers are just relative indicators to help the consumer. In other words, a 5W oil does not have a viscosity of 5, nor does a 30 weight oil have a viscosity of 30. What the numbers do mean is that the viscosity characteristics of a 5W oil are lower than that of a 10W oil. As well, a 30 weight oil has lower viscosity properties than a 40 weight oil. Its all very confusing, isn't it? The best thing to do is use the appropriate viscosity for your engine and climate as recommended by the manufacturer. In general, newer vehicles will specify lower viscosity oils such as 5W-30 while older vehicles will specify higher viscosity oils such as 20W-50. This is because today's engines are built with tighter bearing clearances to take advantage of the fuel economy benefits of lower viscosity oils. It is not really a good idea to use thicker oil in one of these engines because it will disrupt the oil flow characteristics of the engine and may create excessively high oil pressure. In an older engine that was designed with larger bearing clearances, it is appropriate and recommended to use a thicker oil to maintain proper oil pressure and provide adequate bearing film thickness. This is also true for engines that have a lot of miles on them and the oil pressure is starting to drop off. By using higher viscosity oil, you can boost the oil pressure back to normal levels and increase bearing film strength.

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Q: What is the difference between motor oils 5W30 10W30 20W50 and so on?
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