So assuming a water cooloant system, the water is heated and then the question how efficiently can you use this to generate energy? Even the simplest scenerio of pumping this water to a place where hot water is needed and would normally be produced by heating it with gas or elecetricity is a means of producing energy. Wouldn’t probably work here though as the water coolant system is a closed loop so you can’t have water leave the system. It still could pass through another reservoir of water to heat it up which then could be used for other purposes. But don’t know about specifics enough to guess whether or not this is feasible.