What would cause a torque converter to generate excessive heat?

A torque converter generates excessive heat primarily due to internal slippage. When the components within the torque converter, such as the impeller, turbine, and stator, do not engage effectively, it leads to a condition where there is a difference in rotation between the two halves of the converter. This slippage causes the converter to work harder to transfer power from the engine to the transmission, resulting in the conversion of more energy into heat rather than usable hydraulic pressure. As a consequence, the temperature within the torque converter rises significantly, potentially leading to premature wear or failure of the transmission.

Excessive speed, while it can contribute to overheating in some systems, typically does not directly relate to the torque converter's heat generation in the context of slippage. Oil viscosity can affect lubrication efficiency but is not the primary cause of heat from slippage. A leaking drain back valve can lead to issues with fluid levels, but it doesn't inherently cause the internal factors leading to slippage that contribute more directly to excessive heat generation in a torque converter.