What does the gear oil model mean?

I believe everyone has a certain understanding of gear oil, which mainly refers to the transmission oil and the lubricating oil of the rear axle.It can not only lubricate the gears and bearings, but also prevent wear and corrosion, and help the gears to dissipate heat. Then some friends who don't know much about cars will ask, what does the gear oil model represent, and how to choose the correct gear oil model.

First of all, the viscosity of gear oil is based on the American Society of Automotive Engineers (SAE) viscosity classification method, which is 70W, 75W, 80W, 85W, 90, 140, 250 seven viscosity grades, and different viscosity grades are selected according to the seasonal temperature. In addition, the gear oils marked with "W" are winter gear oils. Others are non-winter oil (without the "W" mark). However, many gear oils on the market are universal for all seasons, such as SAE75W-90 and SAE85W-90, which are all classified according to the kinematic viscosity at 100°C.

When we choose gear oil, we must strictly follow the provisions of the vehicle manual and select the appropriate gear oil.If the viscosity of the gear oil is too high, it will not only affect the effect of low-temperature starting, but also increase the running resistance of the engine. If it is too low, it will increase the wear resistance of the bearing and reduce the service life. So if the car is a hyperbolic gear drive axle, you must use hyperbolic gear oil, otherwise it will cause serious gear wear.