I think that the Prius pumps all of the coolant out of the block and into the thermos at shutdown, and then back out of the thermos into the block at startup. I think that that is more involved than what you guys are discussing...
Well.... here's something I just thought of - sorta. So I'm in a heat-mass transfer class (I'm a mech engineering student, yay classes!), and I'm studying for finals and one tidbit is heat capacity.
That got me thinking. We want to store a great deal of heat - not necessarily at a high temperature, just a lot of it. The thermal mass of the coolant, head, oil etc. is huge.
One great way to store heat is to take advantage of latent heat | heat of fusion -- which is heat/energy in solid-liquid phase changes. I need to do some research/calculations - but I suspect 3L of wax will hold more heat than 3L of coolant. I think paraffin wax (yes, I know - fire hazard if exposed) does the solid-liquid phase change around 50C. And I'm sure there's other suitable (albeit less accessible/more expensive) materials out there.
What's great about latent heat storage is that there's A LOT of it. And once you begin the phase change, the average temperature stays constant until the change completes. Now I just need to think of a way to implement - probably VIA some sort of "bucket" heat sink/ heat exchanger.
If anyone here subscribes to Autospeed (a great Aussie motor mag online), they actually talked about a theoretical inter cooler that used wax ("Performal") to basically make your IC a bigger heat sink (because after all, that's what it is for the most part). This idea is backwards to theirs :P
Re-inventing the wheel? Perhaps. Or, perhaps, Toyota's design is an hexagon... and this is a half baked octagon cake
Time is the best teacher. Unfortunately it kills all its students.