What is the difference between gear oil 75w90 and 80w90?

2 Answers
McRosalie
07/24/25 5:36pm
75w-90 and 80W-90 gear oils differ only in viscosity. Below are the viscosity specifications for these two gear oils: 1. 75w-90 viscosity: The kinematic viscosity of 75w-90 gear oil at 100°C is 4.1mm2·s, with a maximum temperature of -40°C to reach 150Pa·s. 2. 80W-90 viscosity: The kinematic viscosity of 80W-90 gear oil at 100°C is 7.0mm2·s, with a maximum temperature of -26°C to reach 150Pa·s.
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SanKayden
08/11/25 9:45am
I've repaired quite a few manual transmission vehicles. The main difference between 75w90 and 80w90 gear oil lies in their low-temperature fluidity. 75w90 flows more smoothly during cold winter starts, with lower viscosity for better gear protection. 80w90 is slightly thicker, making it more suitable for moderate or southern climates. At high temperatures, both maintain the same 90 viscosity rating with equal protective performance. Oil selection depends on temperature: prioritize 75w90 for subzero northern regions to prevent cold-start gear wear, while 80w90 works fine in warmer areas and saves money. I recommend frequently consulting your vehicle manual - mixing oils can cause sedimentation, so always flush old residues before adding new oil. Regular maintenance extends transmission lifespan, saving both money and hassle.
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