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Blowing Hot And Cold: The Role Of The Radiator

When you take a look under the hood of your car, an awful lot of the space in there is taken up with the cooling system – that’s if you’ve got a vehicle that gets its motive power from an internal combustion engine (ICE).  In fact, the complexity and the importance of the cooling system in an ICE vehicle – and the consequences for your car engine if something goes wrong with it – is one of the things that makes electric vehicles look very attractive.

The topic is on my mind somewhat, as last week saw me standing around at the mechanic’s garage looking at a faulty radiator and getting the bad news that my old 4×4 was terminally ill.  It was at that moment that even though I live in a rural area where the range of electric vehicles isn’t practical, I liked the idea of EVs, as they have none of the radiator-related hassles.  (The 4×4 is going to be replaced by a smaller Toyota Camry, as I never took the 4×4 off-road all that much, but that’s another story).

Anyway, enough about me and let’s get onto radiators.

In an ICE vehicle, the rotational motion needed to turn the wheels is produced by a controlled explosion pushing a piston up and down.  If you’ve ever used petrol or diesel to get a sluggish bonfire going, then you’ve probably seen just how explosive these fuels are and how much heat is released.  In fact, quite a lot of the chemical potential energy contained in these fossil fuels – or their biofuel equivalents – is converted into heat energy rather than kinetic (motion) energy.  Actually, probably most of it goes to heat energy, which is why an ICE isn’t a terribly efficient machine, as the amount of energy going in (in the form of chemical potential energy) is nowhere near the amount of kinetic energy going out – and some gets lost as sound energy as well.  For your information, the most efficient machine in terms of the ratio of energy out to energy in is a bicycle… and we don’t really mind if it burns a few more kilojoules in this case.

All that heat energy has to go somewhere or before long, it will melt the engine.  It was heat that got the metal of the engine out of the rocks it came from and into the shape that it is now, after all.  Nobody wants that, so the aim is to get the heat away from the engine and somewhere else where it won’t do any damage.  Most modern engines use a liquid cooling system rather than air cooling, as heating up water soaks up a few more joules. It takes more energy to heat water than to heat air, as we’ve all found out on sunny days in spring when the air is warm but if you try taking a dip in an outdoor swimming pool or the sea, the water still feels like ice.  The solution is to have a bunch of pipes running through and around the engine and these will take the heat away from the engine and somewhere else.  Add in coolant that has an even higher boiling point than water and you can soak up even more heat.

There’s one small problem, and that’s the fact that if water boils, it turns to steam, which, as Isaac Watt noticed with his mother’s kettle all those years ago, expands and exerts a force on what’s around it.  This is how a steam engine works (and makes you wonder if an ICE–steam hybrid is possible: something that relies on the ICE driving the pistons until it builds up a good head of steam and then uses the steam).  However, putting water under pressure increases the boiling point, which is why water boils at low temperatures at altitude.  Of course, too much pressure will blow the hoses as well, so there’s a little regulator that keeps it just right.

If the water stayed put, it would boil quickly, so an extra trick is to keep the water moving.  This is what the job of the water pump is: it moves the water through the system so the water has a chance to shed that heat energy somewhere once it’s away from the business department of the engine.

Once the water has moved away from the explosive part of the engine carrying the excess heat energy, it needs to get rid of that heat before it’s pumped around again.  This is where the radiator comes in.  The radiator has the important job of dissipating the heat energy to the atmosphere.  The core of the radiator consists of a honeycomb of little tubes, usually made of aluminium, which has good heat transfer properties.  The aim of the game is to have lots of surface area to maximise the amount of air that can be exposed to the heat and take it away into the general atmosphere.  To ensure that the air in question goes away from the engine rather than towards it, there’s a fan or two in place to whirr it in the right direction; pretty amazing when you think of the speed at which the car’s travelling.

If the weather is a bit chilly, then the people inside the cabin of the car would actually like to have a bit of that hot air, thank you very much. This is where the car’s heating system comes in.  This takes a bit of the water from the system and puts it through another core – the radiator’s mini-me – and blows it through the vents into the cabin so you can warm up your cold pinkies and toesies – and get the mist off the windscreen so you can see where you’re going.  It’s all interconnected, reminding me somewhat of how your blood circulates.  In the case of my poor old 4×4, the heater suddenly deciding not to blow hot air was the equivalent of a nasty pain in the left shoulder radiating down the arm…

Actually, using your blood circulation system isn’t a bad analogy.  In either case, if there’s a blockage or if something blows because the pressure isn’t right, you’ve got serious, serious trouble.  Blood does indeed help your human engine regulate its temperature and it does this by restricting the flow to extremities when the thermometer does down, which is why it’s your fingers and toes that get cold first.  To get rid of excess heat, the body also does the “increase the surface area” thing, which is why your face gets red when you’re toasty.

Of course, if the weather cold outside and you’re putting on the hats, thick socks and gloves to stop uncomfortable heat loss into the surrounding air, then there’s a chance that the water inside the system will freeze up inside the radiator – as the laws of thermodynamics tell us, heat goes from the hotter thing to the colder thing, even if the “hotter” thing is at 1°C and the colder thing is at –4°C.  Frozen water won’t flow, so you get a blockage in the radiator system, which you don’t want.  It gets worse, too: water expands when it freezes (the only substance to do so) and it can bust any part of the cooling system it fancies in this case.  The solution is to add antifreeze, which has a lower freezing point than water.  Amazingly, the most common antifreeze, ethylene glycol, also acts as the coolant, as it has a higher boiling point and a lower freezing point.

It’s a complicated system – which is why if you haven’t checked the fluids in your engine lately or given the system a proper flush out as part of servicing, then you won’t get as much out of your ICE as you ought to.  Don’t ever neglect this part of car maintenance and don’t say I didn’t warn you!

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