A car exhaust system usually has one important characteristic. The fact that it is capable of keeping poisonous gases safely away from the car's passengers? No. The fact that it can reduce a loud, raucous noise to a tasteful refined humming? No. The fact that it's catalytic converter can trap harmful particles and noxious gases, therefore keeping the environment cleaner? No, it's none of these. The important point is that most people only pay attention to their car's exhaust system when it goes wrong.
Sadly, the notion of the everlasting car exhaust is a mere pipedream. Looking at what a car exhaust has to put up with on a daily basis soon tells us why. Have you ever seen the flames belching from a top fuel dragster with open exhausts? Your car would do the same if it had nothing but open pipes. So from a cold start, a car exhaust system has to cope with temperatures up to about 1400 degrees Fahrenheit (760 degrees Centigrade) at full load. This happens at the exhaust manifold, under the bonnet but the increasing requirement to run engines with a weak (or lean) fuel mixture leads to an increase in car exhaust temperature. For example, if the car has a turbocharger, this can be required to run at 1050 degrees Centigrade (1922 degrees Fahrenheit). Just to give you an idea what this means, 49 degrees Centigrade will burn your skin; your blood would boil at 101 degrees.
Heat isn't all that a car exhaust has to handle repeatedly. The materials that pass through an exhaust system include nitromethane, nitric acid vapour, hydrocarbons, carbon monoxide, sulphur dioxide, particulate matter (i.e. soot and smoke), and volatile organic compounds. Many of these elements are corrosive and the presence of water as a by-product of burning petrol in the engine doesn't make life any easier for the metal of the car exhaust.
So, your car exhaust has to cope with a lot. Is this all? In a word, no. Apart from the heating and cooling cycles and the toxic contents it must deal with, a car exhaust has to cope with mechanical stresses and strains on every journey. A car exhaust is a weighty structure that, at one end, has to deal with an engine that moves about on its flexible mountings. At the other end, the exhaust has to remain fairly still, especially when its tail pipes exit through the car's rear panel. Then there are the demands of speed bumps, potholes and the like. The car exhaust, suspended on flexible mountings over its whole length, has to remain intact under what can be enormous transmitted forces.
The above, which is not overly detailed, constitutes a tall order by anybody's standards. In many respects, it is remarkable that a car exhaust will last for any length of time in the face of the demands placed on it every day. The encouraging news is that a car exhaust can usually be replaced quite quickly, at a good exhaust fitting centre.
Unsurprisingly, you can't do a great deal to give your car exhaust an easier life. You can try to ensure any journey you make is long enough to make the car exhaust hot, which will burn out damaging internal water. You can give the exhaust system a rinse when washing the car, to get rid of corrosive salt. Above all, listen to your exhaust, it'll soon let you know when it's past its use by date. Finally, remember that the 'cat' – the catalytic converter – will need replacing at least once during your car's lifespan.
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