Car coolant cir­cu­la­tion un­rav­elled, stripped bare and ex­plained

Classic Car Weekly (UK) - - Living With Classics - FUZZ TOWN­SHEND CCW’S MAS­TER ME­CHANIC

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’

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