The OEM wax pellet style thermostatic flow control system defaults to cooler flow OFF state. It requires a preheat cycle up to the boiling temperature 100 degC to switch to cooler flow ON state. When it malfunctions cooler flow is bypassed and the ATF and transmission are overheated. This affects pump, valve body, and solenoids, as well as sealing rings and clutch drums operation! The replacement Thermal Bypass Control Valve defaults to cooler flow ON state, which provides instant fill and air purge of cooler and lines so that the accurate fluid level can be established during initial start-up without lengthy warm-up cycle. The default ON state will typically maintain a stable ATF operating temperature of around 70 degC even under working conditions. This extends fluid life, prevents a wide range of over-temp operating malfunctions and helps the control system provide consistent shift and operation control.