Hot water from the engine cooling circuit enters the helicoil
at the top. As it flows down through the coil, it gives up heat
to the stored water in the tank, and returns at a lower temperature
to the engine cooling circuit.
As the stored water heats up it rises by convection. Hot water
is drawn off through the top outlet: cold water flows in at
the bottom of the tank to replace it. If mains voltage a.c.
electricity is available, an electric immersion heater may be
fitted for use when the engine is not running.