If you think a car engine is complex, then wait until you find out what goes on inside the exhaust system! Your car's exhaust system uses a combination of chemistry and physics to make it run in a clean, quiet and dignified way.

It's not hard to notice when your car's exhaust system is no longer functioning. You can smell it, hear it and often also see it. No-one wants the undignified job of driving a noisy smelly car all the way to the mechanic.

So how do your know when your exhaust is on the way out?

If you're getting regular car services by a reputable mechanic, they will usually pick it up in good time and won't let the exhaust become too exhausted!

But how can you tell if you're looking at buying a used car where you can't know that the previous owner had the car serviced properly? You will need to have the exhaust system thoroughly inspected.

Firstly, you will need to understand how the exhaust system works...

Exhaust gas and sound waves from the combustion engine escape through the exhaust valve and into the manifold or main chamber. Exhaust is a hot gas made up of Carbon monoxide (CO), unburned hydrocarbons (HC), and oxides of Nitrogen (NOX). This stinky stuff is bad for people and the environment.

The exhaust gas and sound waves pass through a pipe into the Catalytic converter where it passes through two ducted ceramic blocks. The first ceramic block contains platinum and rhodium. When the hot toxic gas enters this ceramic block the heat causes a reaction causing the oxides of nitrogen to split into oxygen and nitrogen.

The gas then flows into the second ceramic block which contains platinum and palladium where the carbon monoxide and the unburned Hydrocarbons react with the oxygen creating carbon dioxide (CO2) water vapours (H2O) and Nitrogen (N2).

This mix of less toxic gas along with sound waves then travels through a pipe and into the aptly named muffler. The muffler consists of multiple expansion chambers.

Within the first expansion chamber is a pipe dotted with holes. Some of the sound waves exit the pipe into the chamber and bounce off the walls of the chamber. When the chamber is full of sound waves there is reduced space and friction which causes the sound waves to crash into each other cancelling themselves out. More intense sound waves travel into the second expansion chamber, which is smaller and bounce against the walls again, causing the same friction and cancelling out effect.

The loudest of the sound waves make it through the first 2 chambers and into the Helmholtz Resonator. Here the sound waves hit the opposite wall of the chamber and bounce back at the same frequency, again cancelling each other out.

The gas and remaining sound waves travel through on last smaller chamber where friction cancels out any last sound waves before exits the system and enters the atmosphere via the tail pipe.

Usually, the first thing to go in an exhaust system is the muffler. If you hear a constant rumbling sound coming from under the car this could be the sign of a failing muffler.

The biggest cause of problems in an exhaust system is corrosion or rust. This can come from outside the system via rain but it also comes from inside the system with the water vapours in the exhaust.

The best way to check your exhaust system is to simply look at it.

If you see rust it might be time to get it looked at by your local mechanic. If you're assessing a used car to buy, then this is a red flag. A professional vehicle inspection will keep us safe from buying a car with an exhausted exhaust system!