Less known fact: automatic transmission fluid is engineered as both a hydraulic medium and a friction material. Its friction curve is tuned so static and dynamic friction stay close, which helps avoid torque‑converter clutch shudder and keeps shifts repeatable. That’s why mixing ATFs with different additive systems can change shift timing and creep feel even if the grade looks similar. In sub‑zero mornings, the first shifts you notice often reflect the friction package more than thickness. A fluid aligned to that profile, such as Multi Vehicle ATF (TYPE T-IV), also carries detergents, anti‑oxidants, anti‑foam and dye to support reliability.