What is the difference between 75w-85 and 75w-90?
2 Answers
Here are the differences between transmission oils 75w-85 and 80w-90: 1. Viscosity index of 75w vs 80w: Both 75w90 and 80w90 are SAE viscosity grades. Transmission oils can be divided into single-grade viscosity type and multi-grade all-weather type, with the single-grade type further classified into high-temperature and low-temperature types. 75w90 and 80w90 belong to the multi-grade all-weather type, with their difference lying in low-temperature viscosity variation. 2. Operating temperature range of 75w vs 80w: When the ambient temperature reaches -26°C, 80w-90 gear oil should be selected. When the ambient temperature reaches -40°C, 75w-85 gear oil should be chosen. 3. Application purposes of 75w vs 80W: 75w-90 is specifically designed for use in many railway transmissions, while 80w-90 is specially formulated for heavy-duty transmissions, drive axles, and rear axles of commercial vehicles requiring wear and scuff protection.
I've seen many friends asking about the difference between 75W-85 and 75W-90. Simply put, it's about the viscosity of the oil. The 75W part represents the smoothness during cold starts, and both are similar—they won't turn into paste in freezing conditions. The key difference lies in the -85 and -90. -85 is thinner at high temperatures, almost like diluted with water, offering better fluidity, making driving easier and more fuel-efficient. However, it might not provide enough protection when hauling heavy loads at high speeds. On the other hand, -90 is as thick as honey, tougher in hot weather or under heavy loads, with a thicker oil film for better protection, making it ideal for long-distance driving, towing, or older car models. Last time I switched to 85 for city driving, it felt smooth, but trying 90 on mountain roads made the engine noticeably quieter. Remember to check your manual for the specified oil and avoid mixing them based on gut feeling—doing so could damage the gears and cost you more. It's best to perform regular maintenance and change the oil when it darkens. Safety first, after all.
