What is the difference between gear oil 75w90 and 80w90?
2 Answers
75w-90 and 80W-90 gear oils differ only in viscosity. Below are the viscosity specifications for these two gear oils: 75w-90 viscosity: The kinematic viscosity of 75w-90 gear oil at 100°C is 4.1mm2·s, and the maximum temperature to reach 150Pa·s is -40°C. 80W-90 viscosity: The kinematic viscosity of 80W-90 gear oil at 100°C is 7.0mm2·s, and the maximum temperature to reach 150Pa·s is -26°C.
As someone who frequently tinkers with vehicles, I believe the main difference between 75W90 and 80W90 gear oils lies in their performance at low temperatures. 75W90 has better low-temperature fluidity, with the "75" after the "W" indicating it can still flow easily at -40°C, making it suitable for cold regions like northern winters where cold starts won't be too difficult. On the other hand, 80W90 becomes somewhat viscous at -26°C, but it's generally fine in milder climates like the south. Both have the same viscosity of 90 at high temperatures, so their protective performance is similar. If you live in an area with significant temperature variations, I'd recommend using 75W90 as it's more versatile. Don't underestimate this difference—using the wrong oil can make it hard to start your car in winter and cause unnecessary delays. I once saw a friend's car make loud gear noises after using the wrong oil, and the issue was only resolved after switching to the right one. So always refer to your vehicle's manual.
