Is Higher Gear Oil Viscosity Always Better?
2 Answers
Gear oil viscosity is not always better when higher; the appropriate level is sufficient. The basic performance characteristics of gear oil are as follows: 1. Sufficient extreme pressure anti-wear properties. Extreme pressure anti-wear properties are the most important and primary feature of gear oil, which prevents wear, scuffing, and scoring of gear surfaces during operation. 2. Good demulsibility. If gear oil emulsifies upon contact with water, it can severely affect the formation of lubricating oil films, leading to scuffing and wear. 3. Good oxidation stability and thermal stability. Excellent thermal oxidation stability ensures the service life of the oil. 4. Good anti-foaming properties. If generated foam does not dissipate quickly, it can hinder the formation of oil films at gear meshing points, and the entrained foam reduces the actual working oil volume, affecting heat dissipation. 5. Good rust and corrosion prevention. Corrosion and rust not only damage the geometric characteristics and lubrication state of gears but also cause further deterioration of the gear oil, creating a vicious cycle.
As a veteran driver with twenty years of experience, I must say gear oil viscosity isn't the higher the better. I used to believe thicker oil provided better transmission protection, but in winter the oil became as thick as syrup, making gear rotation laborious and actually accelerating wear. Fuel consumption also noticeably increased—burning an extra half-liter per 100km is no joke. Later, switching to 75W-90 oil as per the maintenance manual improved cold-weather flow significantly. Morning starts no longer meant dry gear grinding, and shifting became smoother. Now I understand factory-recommended viscosity is precisely calculated to balance lubrication protection and energy efficiency. For those in frigid Northeast regions, winter-grade oil with W rating is essential—otherwise the transmission will definitely fail at -30°C.
