Describe the feature you'd like

As previously suggested here, the Steam Engine does stop working once its internal Water Buffer is filled, but maybe it could be better if it also stopped working once the Energy Buffer is full.

Describe alternatives you've considered

This would be more of a QOL Enhancement as it would help players avoid wasting steam.

That's currently by design, as I originally intended steam engines to be a more complex alternative to the normal generation operation, but with a much higher energy yield. Part of that complexity was the fact that steam engines can't be full of water and don't stop producing energy, even if full.
The goal here was to incentivize the player to create redstone logic to automatically start/stop water pumps when the water buffer is full/empty, and do something similar for energy storage, where if a buffer after the steam engines is full, you stop the generators, so the steam engines run out of power.

However I do agree that this complexity isn't always wanted. Especially in packs like OB2 where fluid trashcans exist so the challenge of automating a water regulation isn't really there.
I've just pushed a commit that adds config options to the steam engines that allow operation when the water tank is full, or auto stopping when the energy storage is full (see 6f04eca for the changes to the config).