![]() The three classes of ACEA engine oils are listed in bold below. The HTHS viscosity requirements of the European Automobile Manufacturers’ Association (ACEA) are a bit more complicated. Operators should refer to the engine manufacturers’ recommendations to determine if API FA-4 oils are suitable for use in their specific engines. API FA-4 oilsĪre neither interchangeable nor backward compatible with API CK-4, CJ-4, CI-4 Plus, CI-4, and CH-4 lubricants. These oils are formulated to provide enhanced protection against viscosity loss due to shear and areīlended to a HTHS viscosity range of 2.9cP to 3.2cP to assist in reducing GHG emissions. API CK-4 oils exceed the performance criteria of API CJ-4, CI-4 Plus, CI-4, and CH-4 and can effectively lubricate older engines demanding these API Categories.ĪPI FA-4 describes certain SAE XW-30 oils specifically formulated for use in selected four-stroke diesel engines designed to meet 2017 model year on-highway greenhouse gas (GHG) emission standards. API CK-4 oils are designed to provide enhanced protection against viscosity loss due to shear and have a minimum HTHS viscosity of 3.5 cP. HTHS viscosity limits are also incorporated in the latest American Petroleum Institute (API) diesel engine oil specifications:ĪPI CK-4 defines oils for use in four-stroke diesel engines designed to meet 2017 model year on-highway and Tier 4 non-road exhaust emission standards These oils are also suitable for older diesel engines. For instance, SAE J300 specifies an oil must have a HTHS viscosity of 3.7 cP or higher in order to be classified as a SAE15W40 viscosity grade, whilst the minimum limit for a SAE 5W30 is only 2.9 cP. The thinner the viscosity grade, the lower the required HTHS viscosity. It is therefore no surprise that the Society of Automotive Engineers’ SAE J300 Engine Oil Viscosity Classification System includes HTHS limits to ensure that engine oils can be relied on to provide the necessary lubrication under high temperature high shear conditions. Even worse, under high stress conditions permanent viscosity loss may occur due to shearing of polymeric viscosity modifiers. It can also cause lower oil pressure when the engine is idling at operating temperature. Decreased oil film thickness can lead to boundary lubrication conditions and increased wear. Bench tests have indicated that a lower HTHS potentially improves fuel economy at a rate of 0.5% to 2.0% for each 0.5 cP reduction in HTHS viscosity, depending on the engine type and operating conditions.Ī too low HTHS viscosity however may affect engine durability. It should be noted that 1 cP is equal to 1 milliPascal second (mPa.s) since some specifications list mPa.s rather than cP. HTHS viscosity is measured in centiPoise (cP). Under normal operating temperatures (70☌ to 100☌), the HTHS viscosity of engine oil is inversely proportional to fuel economy. The contribution of such viscosity modifiers (VMs) to the viscosity/thickness of oil decreases when the VMs are exposed to the high shear conditions found in critical engine components such as ring/liner interfaces, journal bearings and valve drive components. Multigrade lubricants developed for use in automotive engines often contain polymeric viscosity modifiers. One of the ways that this can be achieved is by using lower HTHS viscosity engine oils. ![]() New global and local government vehicle regulations demand better fuel economy and a reduction in greenhouse gas emissions.
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