Coolant can gain access to transmission through the transmission oil cooler. The oil cooler can leak internally causing the coolant and oil chambers to be linked.
Transmission especially the automatics can overheat. The causes range from bad clutch, wrong fluid, overfilled or underfilled transmission and bad oil cooler.
Modern transmissions are not as simple as they used to be. We can say that transmissions have become smart with the introduction of AI machine learning algorithms
Heat generated from automatic transmissions are transferred to the cooling system for dissipation to the environment through the transmission oil cooler.