During idle in Park or Neutral, which statement best describes the relative motion of the impeller, stator, and turbine?

During idle in Park or Neutral, which statement best describes the relative motion of the impeller, stator, and turbine?

• A. The impeller and turbine are stopped while the stator turns
• B. All three are turning at roughly the same speed
• C. The impeller turns; the stator locks and the turbine stops
• D. The impeller and turbine rotate while the stator is locked

Answer: (B)

When the engine is idling in Park or Neutral, there’s essentially no load on the drivetrain, so the torque converter acts as a simple fluid coupling rather than a torque-multiplying device. The impeller, connected to the engine, pushes hydraulic fluid toward the turbine, which is connected to the transmission input. With almost no torque demand from the wheels, the turbine doesn’t resist the flow strongly, so its speed rises to be close to the impeller’s speed. The stator sits between them and is normally held by a one‑way clutch to give torque multiplication only when there’s significant forward torque. In idle, that forward torque isn’t present, so the stator isn’t held in place and is carried around by the circulating fluid as well. The result is that all three components turn at roughly the same speed, with only a small amount of slip due to internal fluid friction.

When the engine is idling in Park or Neutral, there’s essentially no load on the drivetrain, so the torque converter acts as a simple fluid coupling rather than a torque-multiplying device. The impeller, connected to the engine, pushes hydraulic fluid toward the turbine, which is connected to the transmission input. With almost no torque demand from the wheels, the turbine doesn’t resist the flow strongly, so its speed rises to be close to the impeller’s speed. The stator sits between them and is normally held by a one‑way clutch to give torque multiplication only when there’s significant forward torque. In idle, that forward torque isn’t present, so the stator isn’t held in place and is carried around by the circulating fluid as well. The result is that all three components turn at roughly the same speed, with only a small amount of slip due to internal fluid friction.