hello!
such system already was in serial production in Russia many years ago, name "U.O.P.D." (= УОПД in russian).
designed for improving of starting cold engine in extremally low temperatures, like -30...-40C and lower.
but production was stopped in 2010, i don't know why, becouse idea was good, and was demand for it.
now you can fing another system, "Golfstream".
heat accumulator can be easily removed.
for example, for storing at home in warm.
or for quick refilling by hot antifreese at home.
http://golfstream-nsk.ru/products