What gear lubricant designation is commonly used?

• A. 75W-140
• B. 80W-90
• C. 10W-40
• D. SAE 30

Answer: (B)

Gear oil designations describe viscosity across temperature ranges. The number before the W shows cold-start viscosity, and the number after the W shows how thick the oil is at high operating temperatures. For many buses’ manual transmissions and differentials, 80W-90 is a standard, widely stocked choice because it provides good protection and film strength across a wide temperature range, balancing easy startup flow when cold with solid lubrication when hot.

Other options aren’t as appropriate for gear lubrication. Engine oils like 10W-40 or SAE 30 are formulated for engines, not gear trains, and don’t provide the right additives or performance in gears. 75W-140 is another gear oil grade and is used in some heavy-duty or high-load situations, often with synthetic blends, but it’s not as universally common for everyday gear lubrication as 80W-90.