What is the Difference Between Gear Oil and Engine Oil?

[LeChristian]

Gear oil and engine oil differ in their performance characteristics: Engine oil primarily focuses on low-temperature performance, maintaining good fluidity in cold conditions; gear oil, on the other hand, emphasizes performance under high temperature and high pressure, as the pressure between gears is much higher than in an engine, and the operating temperatures are also significantly higher. Additionally, engine oil is weakly alkaline, while gear oil is strongly alkaline. Engine oil, also known as engine lubricant, serves to lubricate, clean, cool, seal, and reduce friction in the engine, and is composed of base oil and additives. Gear oil, referred to as transmission lubricant, is mainly made up of antioxidants, antifoaming agents, and rust inhibitors, and is used for lubricating various gears in transmissions, reducers, and differentials to prevent wear and sintering on gear surfaces.

[SanAiden]

I've been driving trucks for twenty years, and the main difference lies in their purposes. Engine oil serves the engine, dealing with high temperatures and pressures daily, and it also cleans carbon deposits and metal debris, so it has excellent fluidity. Gear oil, on the other hand, deals with the metal components in the transmission and differential, where there's intense squeezing, requiring it to be particularly viscous to form a protective film. The most obvious difference is the replacement intervals—my old truck needed an oil change every 5,000 kilometers, but the gear oil could last up to 50,000 kilometers. Using the wrong one is a no-go; once, I took a shortcut and added engine oil to the transmission, and shifting gears sounded like stepping on gravel with all the grinding noises.

[StClara]

Last time in the garage chatting about cars with a friend, he mentioned always confusing these two types of oil. I explained to him that engine oil mainly prevents friction-generated heat inside the engine, containing anti-wear agents and detergents to protect moving parts like pistons and crankshafts. Gear oil is more specialized, specifically designed for the hard contact between gears, with a particular emphasis on high-pressure resistance. Just like when we modify cars, gear oil can withstand the instant impact during high-speed gear shifts, whereas regular engine oil would definitely fail. There's also an identification method: smell. Engine oil has a faint chemical scent, while gear oil carries a slight sulfur smell due to the extreme pressure additives added.

[VincentFitz]

My car's maintenance manual clearly states it. The oil grade, like 5W-30, and the gear oil grade 75W-90, show the viscosity difference through the numbers. Gear oil needs to withstand the steel-to-steel squeezing of gear meshing, so higher viscosity is required to stay in place. In the engine, the oil is in a mist state, requiring lower viscosity for faster flow. Last time, the 4S technician said the symptoms of gear oil failure are obvious—if shifting feels rough or there are abnormal noises from the chassis, it needs checking. For engine oil failure, the signs are increased engine noise and higher fuel consumption.

[SawyerMarie]

After ten years in vehicle maintenance, the most common mistake I've encountered is owners using the wrong oil. Engine oil emphasizes cooling functions, circulating to dissipate heat with every start. Gear oil operates in a sealed transmission, facing less cooling demand but requiring higher pressure resistance. Simply put, engine oil is like a marathon runner constantly cooling down, while gear oil resembles a weightlifter bearing heavy loads. Their compositions also differ—gear oil's extreme pressure additives can corrode copper components, making it absolutely unsuitable for engines. Always purchase oil according to the certification standards in your maintenance manual; for instance, GL-5 gear oil must never be used in an engine.