A Close Look at Your Car's Exhaust System

The beauty of the exhaust system on modern cars is that no one thinks about it
for years and years. As long as it does not rattle, make loud noises, or
leak, it does its job quietly and efficiently.
Except for the tail pipe that sits under the rear bumper or behind a rear
tire, the exhaust systems of today are rarely noticed. They are made of
better metals and frequently last deep into the second hundred thousand miles
on most cars. Sometimes, they exceed the life of the car.
The exhaust system begins inside your car's engine. The valves that operate
at the top of each cylinder are responsible for two things. One
responsibility is to let fuel into the cylinder to allow combustion to
happen. The other is to let exhaust exit the cylinder. Each valve or set of
valves performs the appropriate action during the up and down strokes of the
car's pistons.
As the piston moves upward in the cylinder on the exhaust stroke, the vapor
residue from the fuel ignition is forces upward through the open exhaust valve
and into the exhaust manifold. When you look at your car's engine, the
exhaust manifold looks like 4, 6, or 8 arms (usually one for each cylinder)
coming from the sides of your engine and going toward the rear of the engine
where they all intersect into either a single or dual exhaust system.
Inside most exhaust manifolds are two devices. The first is a sensor to make
sure that the burned mixture coming from the cylinder has combusted properly.
This lets your car's onboard computer know if the car is running as it
should. If a problem is detected, the computer will turn on the "check engine
soon" light on your dashboard. This is one of several reasons that this light
may come on.
The second is a damper to regulate the speed with which the exhaust flows from
your engine. This damper serves two purposes. The first is to maintain a
little back pressure on your engine to make it run better. The second purpose
is to help regulate the motors operating temperature. When the motor is cool,
it closes a little to warm it up to the optimum temperature. The opposite
happens if the engine is too hot.
A malfunction in this damper can light up you "check engine soon" warning.
Sometimes as a car ages, this damper can create a rattle inside the manifold.
Usually, this is not a problem, but if the damper sticks open or shut, it can
create the need for a repair job. This always means a new exhaust manifold.
The exhaust pipe fits on the exhaust manifold where all of the arms
intersect. Sometimes there is a gasket at this juncture, but not always. It
varies by model and manufacturer. The exhaust pipe technically runs from the
manifold to the catalytic converter. The catalytic converter serves to remove
most of the hydrocarbon residue from the exhaust.
These converters are why cars today run on unleaded gasoline. Tetraethyl lead
was an octane boosting agent until the 70's. The lead ruined these
converters, and so lead had to be removed from the gasoline. Converters cause
your car to run much cleaner than cars of 30 or 40 years ago. If this
converter fails, your car will run terrible and only about 10 miles per hour.
From the catalytic converter, the intermediate pipe runs to the muffler. It
is only a foot or two in length. The muffler is responsible for keeping the
noise level down. It has baffles inside to divert the exhaust into several
different chambers and dampen the sound from a low rumble to non-existant
depending on the type of muffler installed.
The tail pipe extends from the muffler to the rear of the car. Sometimes it
may have two segments. Hangers along the length of the system keep the tubing
and equipment from falling down or having a distracting rattle.
Most cars today have one set of exhaust equipment. For dual exhaust vehicles,
you just have two of everything. One runs down each side of the vehicle.
Never touch the exhaust while it is hot. Even at the end of the tailpipe, it
can be hot enough to leave an ugly burn on your skin.