What is the difference between gear oil 75w90 and 80w90?
2 Answers
The difference between gear oil 75w90 and 80w90 lies in their viscosity grades: Gear oils are classified into seven viscosity grades - 75W, 75W/90, 80W/90, 85W/90, 90, 85W/140, and 140 - based on their kinematic viscosity at 100°C and the maximum operating temperature when the apparent viscosity reaches 150,000 mPa.s. Relevant information about gears is as follows: 1. Introduction: A gear is a mechanical component with continuous meshing teeth on its rim that transmits motion and power. The application of gears in transmission systems dates back to ancient times. With the development of production, the smooth operation of gears has gained importance. 2. Gear teeth: Each protruding part on a gear used for meshing. Generally, these protrusions are arranged radially. The teeth of paired gears come into contact with each other, enabling the continuous meshing operation of the gears.
After driving trucks for long hauls over a decade, I know gear oil inside out. The main difference between 75W90 and 80W90 lies in their low-temperature performance. The smaller number in 75W means it flows smoothly during cold starts even at -20°C up north, protecting transmission gears from dry grinding. 80W suits warmer southern regions better, performing just right around freezing point in winter. But in summer heat, they behave similarly since both share the same 90 rating. My old rig's transmission insists on 75W90 – once I cheaped out with 80W90 and winter gear shifts felt like stirring thick paste, requiring enormous effort. Now I always switch to 75W90 before winter, and cold starts become noticeably smoother.
