BMWs
turbosteamer was a fairly elaborate engine heat recovery system and only gained them 15% FE sadly. They recovered heat from the exhaust and the coolant. I don't know why it was so inefficient. It seemed like a very well thought through idea.
Considering 2/3rds to 1/2 of gasoline's energy is expelled through the coolant/exhaust this is an area for huge improvements. I'm not sure why more development isn't put into this area. Regenerative braking is great for city driving, and electric hybrids do allow engines to be downsized or atkinsonized, but if you recover half the heat energy from the coolant/exhaust you have the possibility of doubling fuel economy ALL THE TIME.
I like your idea modmonster. I do see some very big problems though. Steam components need to be able to handle lots of heat and lots of pressure. Once we start thinking about the lifespan of the system we really need some beefy components. This starts racking the cost up very fast unfortunately.