A vital part of any vehicle’s engine system is the exhaust system. Ever since the invention of the internal combustion engine, an exhaust mechanism has been needed. The basic 4-stroke automotive engine cycle to turn gas into a piston motion has four strokes making a complete cycle, The cycle is intake (mixture of air and fuel), compression, combustion and exhaust.
The intake cycle begins when the intake valve opens when the piston is at the top of its stroke, and as it moves down in its cylinder it sucks in a mixture of air and a small amount of gasoline vapour. Then the piston moves up in its cylinder and as it does so, the fuel-air mixture is compressed. The compression ensures that when the gas is ignited the explosion is more powerful. As the piston reaches the top of the cylinder, a spark is introduced into the mixture to ignite the gasoline, which then burns rapidly or explodes. This explosion forces the piston down the cylinder rapidly, and is where an engine’s power comes from. As the piston reaches the bottom of the cylinder, the exhaust valve opens to allow the spent fuel and exhaust gas to escape. As the piston rises up the cylinder, the exhaust gas is pushed out of the cylinder into the exhaust manifold.
The exhaust manifold is located on the side of the engine, or on both sides of the engine for a v-cylinder arrangement. Normally a high temperature gasket provides a seal between the engine head and the manifold, with a heat shield installed to provide protection from the hottest part of the engine. Usually the manifold is located on studs and a series of nuts fasten it down, rather than being bolted into the head. An exhaust front downpipe pipe or pipes then connects the manifold to a catalytic convertor, and muffler before the exhaust gases leave the tail pipe. The catalytic converter only works at a fairly high temperature, which is why it is located at the start of an auto exhaust system.
To reduce the amount of pollutants and noxious fumes which escape out of the tailpipe into the environment, a catalytic convertor is usually fitted in the exhaust system into the manifold or front downpipe. This specifically removes reduces emissions of three pollutants found in car exhaust gas – carbon monoxide, hydrocarbons and nitrogen oxides. In the catalytic converter, there are two different types of catalysts which act on the gas, a reduction catalyst and an oxidation catalyst.
After the convertor, the final stage is the muffler where exhaust gases go through a series of perforated tubes inside baffle chambers to weaken the sound created during the combustion process , so the sound is quietened or deadened before leaving through the tail pipe.
The exhaust system of most vehicles is typically not looked at during normal driving unless there is a rattle or the muffler is blowing. The exhaust system is designed to move waste and burnt gases from the cylinder head from the exhaust manifold through pipes to a catalytic converter and eventually a muffler before exiting the vehicle with air pollution and noise greatly reduced.
At a good auto repair shop, the recommended service interval for an exhaust system check is every 20,000 miles. This is just often enough to prevent any unexpected failures, but is not usually needed too often under normal driving conditions. If however the vehicle is driven off-road or over obstacles which could cause an impact underside the vehicle, then a shorter service interval would be recommended.
As the exhaust is directly connected to the engine, before any service checks take place, normal practice is to let the car cool down for at least an hour or so. One of the best ways to check a mounting or bracket is to move the pipe from side to side, and this is obviously easier to do if the system is cold.
20,000 miles Routine Service Check
A full system check goes from the engine to the end of the tail pipe, and due to the usual exhaust layout is better performed from underneath the vehicle while the car is on a lift in a bay. The exhaust pipes and connections are inspected for signs of leaks, corrosion and damage. A leak can normally be seen by a visual inspection because there will be telltale signs of a black sooty stain around the leak.
All brackets and mountings are then checked, ensuring all mounting nuts and bolts are tight. In order to reduce vibration, most of the exhaust mounting brackets are connected to the exhaust itself with a rubber or fiber flexible joint – these can deteriorate over time (and wear can be accelerated due to exhaust heat). If any coupling shows sign of wear, this would be a good time to replace the mounting at low cost to avoid a breakdown on the side of the road. See the picture showing a flexible mounting of the muffler at the tail-pipe end. The yellow arrow points to the flexible mount to be tested.
Finally the exhaust pipes can be checked for rattles by pulling on them from one side to the other – if any contact is made with the body or suspension parts, then the system can be adjusted or a worn mounting can be replaced to avoid any unnecessary rattling noises as the vehicle is being driven over an uneven road. These simple routine checks at your auto service center can help keep your vehicle running smoothly.
For auto service in the Plano Texas area, contact:
Mastertech Auto Care
900 West 15th Street, Suite B
Plano, TX 75075
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