What is the difference between engine oil and gear oil?

[McMila]

Gear oil and engine oil differ mainly in the following aspects: 1. Different working environments: Gear oil is mainly used in manual transmissions, reducers, and differentials, while engine oil is primarily used in car engines. Since gear teeth engage through line contact, gear oil must have extremely high viscosity specifications; otherwise, it cannot form an oil film at the gear engagement points. In contrast, engine lubrication points mainly involve surface contact without the extreme high pressure generated by gear engagement, so their viscosity requirements are relatively lower. 2. Different focuses: Gear oil emphasizes protecting gears under high temperatures, while engine oil prioritizes low-temperature fluidity. Moreover, gear oil is strongly alkaline, whereas engine oil is weakly alkaline. 3. Engine oil and gear oil must never be mixed, as this can easily prevent machinery from achieving optimal lubrication and cause damage.

[DonovanRose]

Over the past few years, I've been working on my own car repairs for fun, and I've learned that engine oil and gear oil are quite different. Engine oil is specifically designed for engines, lubricating components like pistons and bearings, and it also helps clean internal carbon deposits. It needs to withstand high temperatures, remaining stable even when oil temperatures exceed 100°C during normal driving. Gear oil, on the other hand, is used in manual or automatic transmissions—it's thicker, almost like honey, and primarily protects gears from wear under high-pressure engagement, such as during gear shifts where impacts are significant. The viscosity of gear oil helps prevent damage. The additives differ too: engine oil contains anti-wear components, but gear oil has stronger EP (Extreme Pressure) additives to withstand shocks. Mixing them up can cause major issues. Adding gear oil to an engine would make moving parts sluggish, while using engine oil in a transmission would cause it to burn off quickly. That’s why I always check the manual and use the specified oil during maintenance—it saves me a lot of repair headaches.

[PatrickDella]

When I had been driving for less than a year, I often couldn't tell the difference between engine oil and gear oil. Now I understand. Engine oil is used to lubricate all the core components of the engine, ensuring smooth operation and preventing overheating. For example, changing it regularly, like every six months or 5,000 kilometers, is necessary. Gear oil, on the other hand, serves the transmission. It's thicker and more pressure-resistant, specifically designed to handle the high shear forces of rotating gears. My manual transmission relies on this for smooth shifting. In terms of viscosity, engine oil with an SAE rating like 5W-30 is thinner, while gear oil, similar to 80W-90, is much thicker. The oil change intervals also differ—engine oil needs more frequent changes, whereas gear oil typically lasts 20,000 to 30,000 kilometers. Using the wrong oil poses serious risks: putting gear oil in the engine increases fuel consumption, while using engine oil in the transmission accelerates gear wear. Always check your vehicle's manual or consult a professional shop for recommended oils—developing this habit makes maintenance effortless.

[JamesonDella]

Reflecting on decades of driving experience, engine oil and gear oil serve distinct purposes. Engine oil is used inside the engine to lubricate moving parts and also handles heat dissipation and cleaning. Gear oil, on the other hand, is solely for the gear components in the transmission—like those in older manual gearboxes, where the oil is as thick as glue to withstand the high pressure from gear friction. The viscosity difference is notable: engine oil flows well to adapt to high-temperature conditions, while gear oil remains thick and resists thinning. Mixing them can cause issues—there were cases in the past where using the wrong oil led to engine knocking or rough gear shifts. Regular oil changes are crucial, but gear oil intervals are longer. Always use the correct oil to ensure smooth driving.

[VanColeman]

As a daily driver, I focus on practicality: engine oil and gear oil differ significantly in cost and application. Engine oil is common and inexpensive, requiring frequent changes to lubricate the engine and prevent overheating, keeping maintenance costs low. Gear oil is pricier but replaced less often, specifically designed for transmissions to withstand high pressure and protect gears. Mixing them up causes serious issues—adding gear oil to the engine can make parts sticky and increase fuel consumption, while using engine oil in the transmission accelerates wear, leading to costly repairs of thousands. The right choice: engine oil for engine lubrication, gear oil for transmission operation. I always follow the manufacturer’s manual for specified oils, avoiding cheap substitutes. Regular maintenance extends part lifespan and saves money and hassle.