WATER PUMP EVERYTHING YOU NEED TO KNOW
Car coolant circulation unravelled, stripped bare and explained
n the earliest days of the I motor car, water pumps were rarely seen in engine bays, coolant circulation being achieved by means of thermosyphon – the circulation of liquid coolant set in motion by engine-generated heat.
Combustion heat transferred into the coolant and thus the hot liquid rose, entering the radiator at the top and cooling on its passage through the tubes, exiting at the bottom before re-entering the engine.
This system was all very well in cars featuring relatively low compression engines that were unlikely to be stuck in traffic for any amount of time. It was, however, disadvantageous when encountering hills, because, as the vehicle slowed, so did the progress of cooling air passing through the radiator, leading to the coolant water boiling.
Enter the water pump, driven by gear or, more often, a leather or rubber belt from a pulley on the nose of the crankshaft. This accelerated the circulation process and kept the coolant on the move, meaning that a greater volume of coolant was passed through the radiator in a given time and so, even when air was passing through slowly, it was cooling more of the liquid.
The water pump pulley also became a convenient place to site a cooling fan, a component not always found on thermosyphon systems, thus increasing airflow volume through the radiator.
Pressurising the coolant was the next step for car engines, allowing the liquid to achieve temperatures above its atmospheric boiling point, but necessitating greater coolant flow through radiators featuring a greater amount of finer tubing.
As a result, the water pump – once a luxury – became an essential item in car manufacture. In time, another regular additional extra piece of equipment meant that the water pump became absolutely indispensable. Heaters and demisters added a secondary coolant circuit and so efficient, high-volume water pumps became the norm.
Brass was a regular metal early on. However, brass was expensive and so cast iron became more commonplace, sometimes featuring brass impellers, but even these later succumbed to all-conquering iron.
Later classics began to use pumps made from aluminium, especially once dedicated, anti-corrosive coolants had replaced ordinary water. Finally, heat-resistant plastics took over as the easiest and cheapest material of all from which to manufacture the components.
Though belt drive remained the most common form of water pump propulsion, over the years other methods included hydraulic and electric motors. However, no matter what the drive or material, the basic componentry of the water pump has remained the same for many decades – a finned impeller rotates within a chamber, drawing coolant in through the central inlet and expelling it through the outlet and through the engine using centrifugal force.
Some of the coolant circulates around the heater circuit, but it all ends up at the radiator’s top inlet. The water descends as it cools and exits via the bottom outlet and thence back to the centre of the pump.
‘Once a luxury, the water pump became an essential item in car manufacture’