: This is a critical warning sign that engine coolant has leaked into the transmission, often due to a failing radiator or cooler. Maintenance Importance Keeping the fluid "red" is vital for: Lubrication : Reducing friction between moving metal parts.
: The fluid is new or in excellent condition.
: Providing the force necessary to shift gears in automatic systems.
Transmission fluid is dyed a distinct, bright red by manufacturers for two main reasons:
: The fluid is oxidized and burnt. This often indicates a high level of heat or internal wear.
The shade of "trannies red" tells a story about the state of the gearbox:
: The translucent red color allows vehicle owners and mechanics to visually inspect the condition of the transmission system. Fluid Condition Guide
: The fluid is beginning to age and may need a "drain and fill" soon.
