This is a measure of a fluid's resistance to flow. Which factors should you take into account when choosing the right engine oil? Viscosity OEMs, moreover, are adjusting their lubrication instructions faster and faster to comply with the need for green and fuel-saving alternatives. Engines often need a different viscosity depending on the operating conditions. They are designed to provide fuel economy without sacrificing engine protection in a range of applications.įor example, for a specific heavy-duty engine, switching from a 15W-40 CK-4 oil with a 3.9 cP HTHS viscosity to a 10W-30 oil with a FA-4 (2.9 cP) HTHS viscosity provides a fuel economy improvement of about 1% in high-speed, high-load driving conditions and up to four percent at low-speed, low-load driving conditions.Often, a manufacturer will suggest one or more viscosity values for an engine such as 5W-20 or 5W-30 based on different factors including the temperature and load. FA-4 XXW-30 oils have HTHS viscosities between 2.9 and 3.2 cP, which help to enhance fuel efficiency further. The minimum HTHS viscosity for (XX) W-30 CK-4 oils is 3.5 centipoise (cP). Even within a viscosity grade, differences in HTHS viscosity could affect fuel economy. Switching to a lower viscosity grade SAE oil, for example, from a 10W-40 to a 10W‑30 oil, will provide modest fuel economy benefits. The stated viscosity of an oil does not represent an exact viscosity, but rather a viscosity within a range on the Society of Automotive Engineers (SAE) viscosity scale. Low shear kinematic viscosity (KV100) contributes to the definition of monograde oils and provides a viscosity range for high-temperature viscosity grades in multigrade oils. HTHS dynamic viscosity contributes to the SAE viscosity grade definition (for example, the 40 in 15W-40). Low-temperature pumping and cranking viscosities define the winter grade (for example, the 15 in 15W-40). SAE oil viscosity grades are defined by four different tests. Therefore, you could have two separate 10W-30 engine oils produce two different results in fuel economy. Engine oils closer to 9.30 cST will provide better fuel economy benefits than oils closer to 12.49 cST. For example, 10W-30 engine oils can fit anywhere in the range of 9.30 cST to 12.49 cST. “W’ grades, or the number before the “W” in the SAE viscosity, are measured at 40☌. SAE engine oil viscosity is measured in centistokes (cST) at 100☌. HTHS is seen as a more accurate method for measuring viscosity. One such method is called the high-temperature, high-shear (HTHS) viscosity (defined as an oil’s resistance to flow under high-stress conditions at operating temperatures) that distinguishes CK-4 oils from FA-4 oils for modern engines. There are different types of viscosity measurements that can be used to describe and measure the viscosity. Lower viscosity oils pump more easily and help to reduce engine friction, which can improve fuel economy. truck increasing its fuel economy by just 1% would see an annual reduction of over four million tons of carbon dioxide emissions, which is the equivalent of removing more than 20,000 trucks from the road. Even the smallest increases in fuel economy can result in significant reductions in fuel consumption and carbon dioxide emissions.
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