Car Mechanics (UK)
Everything you need to know about fixing and replacing your vehicle’s exhaust system.
In the early days of motoring, a typical exhaust system was responsible for not only carrying toxic emissions away from the passenger compartment but also reducing the noise caused by the gases escaping the engine at high velocity.
“Today, these are not the only functions,” says Doug Bentley, technical head of research and development at Klarius Exhausts of Cheadle, Staffordshire and our technical adviser for this feature. “Aside from influencing engine efficiency, the modern exhaust system is crucial to pollutant control and curtails the emissions of hydrocarbon (HC), nitrous oxides (NOX) and particulates (PM).”
The times they are a-changin’
A vehicle’s original exhaust system is designed to complement the engine, enabling it to meet the emissions requirements set by the Euro Standards of Whole Vehicle Type Approval. It also influences performance and fuel economy.
“A replacement exhaust system must perform to the same standards, at the very least, to those met by the original system,” says Doug. “It is possible for a low-grade replacement to cause a car to produce higher than intended emissions, or cause the engine malfunction indicator lamp (MIL) to illuminate, thereby increasing the likelihood of an MOT test fail.”
Due to lack of legislation in the UK, many exhausts sold and fitted are not tested and approved thoroughly. Most drivers are completely unaware that their ‘bargain’ exhaust system can be a false economy in the long run, due to it incurring extra fuel costs. The exhaust system also maintains an optimum amount of back pressure, which is critical to power, economy and pollution control.
In recent years, exhaust-mounted after-treatment systems have been fitted to lower the expelled quantity of harmful gases that are released into the atmosphere. These include not only treatment hardware, such as catalytic converters, gasoline/diesel particulate filters (GPF/DPF), EGR valves, NOX traps and SCR (Adblue) systems, but also monitoring equipment such as Lambda/oxygen and pressure differential sensors that feed electrical signals to the engine ECU.
The proliferation of car models and engine choices has also affected the replacement exhaust buying process, as Doug explains: “As a longstanding emission control products manufacturer, gone are the days of us making several part numbers in large quantities. Now, we sell a similar number of systems, but over a hugely expanded parts range. We develop around 250 new exhaust systems annually. Original exhausts now last longer and get replaced less often but, to counteract this, the variety and number of cars has increased. We now sell a more diverse range of products, of a higher technical complexity.”
The explosion of different part numbers, often with very subtle changes between different specifications of the same basic car model, makes it more likely that you and your supplier will source the wrong part. Klarius reports that 80% of calls that it receives through its customer helpline are due to the incorrect parts being ordered. If the motor trade is getting it wrong, then the relatively inexperienced DIYER is also likely to make a mistake.
“Take the Vauxhall Vectra 1.8 petrol,” says Doug. “It may have one engine water pump listed, but the same model may have 20 different options for the exhaust.”
Exhaust components are also very difficult to catalogue. Klarius finds that motor factors can make incorrect assumptions, when taking an order. Although you might think that an exhaust that has been identified by a vehicle numberplate will be exactly right, things are not quite that simple. Not only might the exhaust catalogue exclude all of the various options, but the salesperson might also select the wrong part number, or the first one, listed on the computer screen.
When ordering, it’s helpful to provide additional details. Exhausts might be shaped differently for different body formats of the same model – saloon, estate or hatchback, for example – while catalytic converters, or DPFS, might have different precious metal contents between Euro III/IV/V emissions standards. Even mentioning that your car has a chrome tailpipe trim will help secure the correct part.
Despite exhaust systems lasting longer than they did on cars made 20 years ago, Doug says these new technologies have presented business opportunities for Klarius, because it is not common knowledge that burning a gallon of petrol produces, approximately, the same quantity of water, which collects mainly within the exhaust system. As hybrid engines tend to switch themselves off, their exhaust systems tend to run cooler, providing less opportunity for the moisture to escape. Instead, it condenses into an acidic liquid and corrodes the exhaust system from the inside out. It is no coincidence that one of Klarius’s most popular replacement systems is for the Toyota Prius.
Falling off the perch
Despite Klarius’s ethos of stocking exhausts for every make and model, vehicles no longer in production have to be delisted at some point, which tends to be when there has been zero demand for two years.
“Take the Vauxhall Corsa B as an example of how demand decreases as more vehicles are scrapped,” explains Doug. “We used to sell 2000 back silencer boxes for that model every month. Now, the figure is around 60.”
While Klarius maintains an exhaust stock for older models, a new batch is not commissioned once it has been depleted and the tooling is either archived, or scrapped. This decision is made on a case-by-case basis. For example, while British Citroën XM exhaust sales are low, this is not the case in France. Should your car have a delisted system, Doug says that the best alternative is a manufacturer of bespoke systems. Most of those specialists offer either mild, or stainless-steel options. However, be aware that stainless-steel also has limitations. While the material is more corrosion-resistant, it is also more brittle than mild, or aluminised, steel and cracks tend to be prevalent, especially on bends and welds. Additionally, the quality varies, so some of these fit-for-life systems may last longer than others. The best advice is to seek a respected manufacturer that makes exhausts from the more expensive but superior 304-grade of stainless-steel and to read any warranty conditions very carefully.
This advice also applies to off-theshelf exhausts. As Doug explains: “Klarius systems, for example, have a warranty of up to three years. Yet we make it a stipulation that all rubbers and mounts are replaced; otherwise, the new exhaust system might be exposed to more vibration and stress than is expected under normal conditions. The majority of sellers retail replaceable mounts under different part numbers, so check that they are supplied with any new system.”