What is the difference between 75w-85 and 75w-90?

[LaMila]

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.

[MacVictoria]

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.

[McSamantha]

Let's talk in depth. The viscosity difference between 75W-85 and 75W-90 is reflected in the high-temperature values. In the SAE standard, 85 is the low-viscosity grade, while 90 is the high-viscosity one. Both have the same 75W low-temperature rating, ensuring no slippage during cold starts. Using 85 oil makes the car feel more agile, with less engine burden and potentially better fuel efficiency. The 90 oil is thicker, offering stronger load-bearing capacity, making it ideal for off-roading or high-speed driving where oil film breakdown is a concern. I always emphasize not to switch oils blindly—using low-viscosity oil under high loads may accelerate gear wear. Checking the car manual is the safest bet. Generally, 85 is sufficient for daily driving, while 90 is better for performance cars. The impact on fuel economy is minimal—85 might save around 0.5L of fuel, but 90 offers longer oil life. Regular maintenance is key to peace of mind.

[McEzra]

Choosing between 75W-85 and 90 boils down to cost-effectiveness and usage. The thinner 85 may be slightly cheaper, offering better fuel efficiency and eco-friendliness with lighter driving feel. The thicker 90 costs a bit more but provides superior durability under heavy loads, protecting gears from damage. I've seen cases where wrong oil choice (e.g., using 85 for mountainous heavy-load driving) led to costly gear repairs. Always follow the owner's manual: opt for 85 in new cars or daily commutes for savings and efficiency; for trucks/off-roading, invest in 90. Temperature matters too – 90 offers steadier protection in heat. Regularly check oil levels and replace if darkened. Proper maintenance ensures vehicle longevity with minimal hassle.