Torque Converter Stator
The stator clutch is located inside the vehicle’s torque converter. It’s critical to the operation of the torque converter and the overall drivability of the vehicle. During low speed operation, the stator locks, creating a vortex. This vortex results in torque multiplication. The stator remains locked until the torque converter reaches its coupling phase.
This is a point in the torque converter’s cycle where the turbine (attached to the transmission) reaches 90% of the impeller's (attached to the engine) speed. At this point there is no more torque multiplication and the stator is allowed to spin freely. An overrunning clutch allows the stator to spin freely in one direction and keeps it from rotating in the other.
If the stator's one way clutch is faulty and allows the stator to spin freely while at low speeds, there will be a loss of torque multiplication, resulting in poor low speed performance. On the other hand, if the stator’s clutch freezes up and remains constantly locked, the vehicle will suffer poor high speed performance.
This will result in overheating of the torque converter and will be evident, because the converter’s hub will turn dark blue. A little blue discoloration around the hub is considered normal, but dark blue/black is not.
A good way to check for normal operation is to place the converter on a bench and use your fingers to rotate the stator inside of the shell. It will be splined and should spin freely in one direction and should lock up in the other. If it spins freely in both directions or if it’s locked in both directions, the torque converter must be replaced.