What are the types of automotive transmission fluid?
3 Answers
Depending on the structure of the automotive transmission, transmission fluid can be divided into automatic transmission fluid (ATF) and manual transmission fluid (also known as gear oil). Automatic transmission fluid is specifically designed for automatic transmissions. Widely used ATF models include DEXRON, DEXRON-II, and DEXRON-III. The DEXRON standard is classified according to the standards of General Motors (GM) and is the most widely applied standard. Performance requirements include low-temperature fluidity, high-temperature oxidation resistance, foam resistance and gas release properties, and rubber seal compatibility. Gear oil can be categorized into performance grades such as GL-1, GL-2, GL-3, GL-4, GL-5, and GL-6, with corresponding grade markings on the packaging. Among these, GL-1, GL-2, and GL-3, which are more focused on heavy-duty applications, have been phased out in the market, while GL-4 and GL-5 are commonly used in household vehicles today.
I do have experience talking about transmission fluid, having changed three cars myself. Manual transmissions use gear oil, similar to the old-fashioned mechanical gears with grease, mainly to prevent wear and resist high temperatures. Automatic transmissions are more complex—AT transmissions require ATF (Automatic Transmission Fluid), which not only lubricates but also transmits hydraulic power, so its flow properties are unique. CVT transmissions need specialized fluid with special friction modifiers to prevent the steel belt from slipping. Dual-clutch transmissions come in dry and wet types, with the wet type requiring a fluid that's like a mix of ATF and gear oil, as it must also cool the clutch. Nowadays, many hybrid vehicles have transmissions connected to electric motors, so the fluid must also be insulating and resistant to electricity. Using the wrong fluid can seriously damage the transmission. I once used non-standard fluid myself, and the gear shifts were as jerky as a roller coaster ride.
Anyone into car mods knows that choosing the wrong transmission fluid can ruin your ride. Regular ATF for automatic transmissions needs Dexron or Mercon certification—thick like honey but stays stable at high temps. Manuals use GL-4 or GL-5 gear oil, basically a hot spring for gears. The biggest headache for performance fans is DCT fluid—wet clutches bathe in it, so low friction coefficient is a must, or you’ll get jerky shifts. I’ve seen clutches burn up at track days from wrong fluid—the whole paddock reeked of burnt toast. CVT fluid is the fussiest, with friction specs dialed to 0.001. A buddy cheaped out with ATF, and his belt started slipping at just 2,000 km. Hybrid trans fluid? Check the insulation rating—high-voltage motors sit right next door.
