The Thermosyphon Engine

Up to the 1930s internal-combustion engine automobiles - opposed to battery-electric or steam - used what was known as the thermosyphon type cooling system design method.  The thermosyphon method relied upon convective cool water induction into the hot engine to keep critical heat sensitive components cool as a means of dissipating heat and prevent premature, accelerated or excessive wear or damage, such as seizing.


The thermosyphon engine relied upon the principle of thermodynamics or Newton's Law of Cooling.  Below is the processed expressed in a mathematical formula.  (Image from Virtual Lab -

The cooling system design of the thermosyphon engine, sometimes spelled thermo-siphon, was not all that different than those that followed, including today's with the exception of the Wankel engine and current motor cooling systems being closed and coolant pressure forced for circulation.

And, as the included illustration shows engine heated coolant, usually just water  during the early period when motometers were most commonly used, rises from the heated area(s) of the motor exists at its top and into the top of the radiator tank where it is cooled by moving air fast flowing through the radiator cooling fins (aided by the then usual pulley-driven radiator fan) cools becoming more dense then sinks to the bottom of the tank to start the induction and re-heating/circulation cycle all over again.






The Above image originally appeared in Motor Age trade journal, Volume 42, Issue Number 18, Chicago, November 2, 1922, page 27.

Early on these engines were more commonly referred to "Heat Motors" owing to thermodynamic engineer observances and naming convention.  Heat motors are those that produce excessive heat, usually through the internal-combustion energy production process.

Newton's Law of Cooling Formula on
Thermosyphon Engine Cooling Circulation System Illustration on



SINCE 1912