Keeping the heat out
In the peak of summer, here’s how your car stays coolindia Updated: Aug 28, 2009 11:23 IST
Internal combustion engines convert heat energy into motion by igniting fuel and air. They aren’t very efficient, if you consider absolute efficiency — about a third of the actual energy available in the fuel makes it to your wheels and performs useful work. The rest escapes as an offering to the gods of heat transfer and friction. Even so, they function best when they’re within a particular temperature range.
Cars are used in all sorts of conditions — you might think that things like heated mirrors and headlamp washers that shoot warm water onto the headlamp lenses are frivolous, but the people in Norway and Alaska would beg to differ. They, however, might think that sun film and a really powerful air-conditioner doesn’t make much sense!
Since manufacturers today are developing global cars, the one model they produce has to be able to run reliably in any place, from the heat of Death Valley to the cold of the Arctic Circle. Since engines run at optimum efficiency within a particular heat range, they have systems to keep the temperature in check.
Glow plugs and coolants
Cold starts can be a bother if you’re experiencing sub-zero temperatures, so diesel engines have something called ‘glow plugs’ which heat the cylinder walls enough to let combustion keep going early in the morning. If you have a diesel car, look carefully at your dashboard when you turn your key to the ‘on’ position. There will be a glowing spring that turns off after a short while. That’s the sign for the glow plugs, or ‘heater’ as the local mechanics call it.
We relate better to an overheating engine with the kind of summers we have. To this end, engines have coolant running around in the engine block and head (the bottom and top) to help maintain its temperature. The coolant duct is like a tunnel that runs through the block, then out through a pipe to the radiator that is usually placed at the front of the car, because that’s where the air is the coolest, and when the car’s moving, that’s also where you get the most cooling. The radiator is nothing but a device to give heat out to the air and to bring the temperature of the coolant down. If you’re stuck in traffic a lot, there won’t be enough fresh cool air rushing to the radiator to keep things in check, which is why an electric fan is attached to it on the inside. This fan makes sure that the radiator gets enough air if the temperature gets too high. It will run even if your car is turned off and locked, so don’t worry if you can hear it while walking away from your car.
Follow these precautions
Coolant is usually under pressure so that it doesn’t boil easily. A gas won’t flow like a liquid will, and neither will it absorb and give out heat as effectively. Since engines usually run at over 700 degrees Celsius, that pressure is necessary. Do not open the radiator cap while the engine is hot, you’ll run the risk of burning yourself. Coolant used to be mixed with alcohol to prevent its freezing in sub-zero temperatures, but today’s liquids are specially developed, so distilled water and alcohol won’t do any more. You’ll know if you’re leaking coolant as it is a green liquid — those of you who have been in a front-end shunt and have damaged your radiators know this for sure!
Correction: My thanks to Phiroze for pointing out an error in my reply to Haresh’s question last week. He correctly says that all transverse-mounted engines (all front-wheel-drives) have electric fans, not belts.
My apologies to Haresh, who probably got really worried when he went to check his radiator fan’s belt, and discovered there wasn’t one.