The highest operation temperature in spur gears is about 130☏ (54☌). 5 grade gear oils for reducing friction and wear and oxidation stability. Pour point of syntethic oils may reach -50☏ (-46☌). These fluids are compared with commercially available API GL. Mineral oils possess relatively high pour point - about 20☏ (-7☌). The American Petroleum Institute, which sets standards for lubricants, classifies gear oils using ratings: GL ratings. The low temperature limit of a gear oil is 9☏ (5☌) higher than its pour point (the lowest temperature, at which the oil may flow). Viscosity of a gear oil depends on the temperature, therefore an oil selected for a particular gear should provide its reliable operation within the expected temperature range. Interestingly a 90-grade gear oil viscosity falls between a 40 or 50 grade. The higher numbers of a gear oil (e.g., 75W-140) do not mean that it has higher viscosity than an engine oil.
#Gear oil weight explained manual
High viscosity provides thick oil film, high wear resistance and low galling even at high pressure (EP). The SAE has a separate viscosity rating system for gear, axle, and manual transmission oils, SAE J306, which should not be confused with engine oil viscosity. A higher viscosity represents a higher weight oil. High viscosity is favorable for: low speed, highly loaded gears with a rough tooth surface. The weight of a differential fluid is determined by the viscosity of the fluid.
Low viscosity provides thin oil film, low friction (high mechanical efficiency), good cooling (heat removal) conditions. Low viscosity is favorable for: high speed, low loaded gears with a good tooth surface finish. 80W transmission oil and 50 weight engine oil) or they can be. Viscosity of gear oils (lubricants) is a compromise between the gear parameters requiring low viscosity and those requiring high viscosity. Oils can either be mono-grade meaning they only claim to meet one viscosity specification (ie.
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