I used to install "tank heaters" to keep the whole engine block thinking it was springtime. They attached at the base of the radiator with a hose circling back up and into the engine. You'd plug it in, it'd heat the water which would naturally rise up and go into the engine. Then, when you started the car (which was easy since it was already warmed up), you could immediately turn on the heater. Wonderful device. Made me the envy of neighbors around here that never had heard of them before.