Within your car’s exhaust system there are two areas that are hot spots for trouble and often need cleaning – the catalytic converter and the diesel particulate filter. Both of these cause problems for the efficient running of your car and can lead to it failing its MOT. In fact, Britain has a monthly peak of 43,000 cars failing the annual roadworthy test because of unacceptably dirty emissions from the exhaust.
Given the high cost of replacement parts, it’s no surprise that many drivers are embracing DIY cleaning products. These claim to return to good health congested catalytic converters or diesel particulate filters. We look at the options for drivers and ask whether they are worth using.
What causes the problems for catalytic converters and diesel particulate filters?
The catalytic converter (cat) fitted to an engine is there to take the harmful chemicals created in the combustion process and turn them into harmless ones. Through the life of a car carbon deposits build up inside the cat meaning it doesn’t work as efficiently and, over time, this increases the harmful emissions coming out of the exhaust – one of the key elements tested in the MOT. On modern diesel-powered vehicles there is a particulate filter (DPF) in the exhaust system that does a similar job but removes and stores a greater number of particulates ahead of the cats.
If you don’t know whether your diesel car has one fitted, telephone a franchised dealer and they will be able to tell you. It’s worth noting that if your car is relatively new and still under its manufacturer warranty, drivers should consult a franchised dealer before taking any remedial action themselves.
The modern diesel engine is designed run a ‘regeneration cycle’ where it burns off the accumulated deposits, but if the DPF is excessively clogged this won’t happen and a garage will most likely suggest replacing the whole unit, which is very costly, with prices often over £1,000.
Some experts suggest that problems with cats and DPFs are made worse by using low quality fuel, often from non-branded filling stations.
About DPF and catalytic converter cleaning products
Generally, both do-it-yourself and aftermarket cleaning products are additives consisting of varying chemicals that pass through the combustion process and then break down the harmful deposits in either the DPF or cat. These can then be passed through the system and expelled out of the exhaust. They are claimed to cause no damage to other parts of the engine.
What do they cost and how do you use them?
Let’s start with the cheaper, and therefore more popular, do-it-yourself cleaning products. These compact bottles of fluid can be bought from reputable motor spares stores or online, and you simply pour the liquid into the car’s fuel tank, much like filling the car with fuel.
Catalytic converter cleaning additives, such as Cataclean, are around £15-20, whereas the DPF cleaning additives such as Wynn’s DPF Cleaner is around £10 from Halfords. Cataclean also offers drivers a diesel version that cleans both the DPF and cat and costs around £20. All of these additives are used by simply pouring them into your fuel tank and driving the car in the usual way for 15-30 minutes. Most advise a specific ratio of fuel to additive on the bottle, so always read the instructions before using the product.
Do garages clean exhaust systems?
More and more garages offer an exhaust cleaning service. One option is called Terraclean which is a patented cleaning system that tackles everything from the fuel injectors right to the exhaust tip. It can only be administered by an approved garage, but there are over 450 across the UK. It costs between £110 and £130, depending on engine size.
Halfords Autocentres offer a diesel particulate filter cleaning service, and charge £35 for a ‘maintenance clean’ and £85 for a ‘deep clean’. The company adds that in the unlikely event that either of the treatments fail to work, it will deduct the cost of the treatment from the servicing bill.
Do they work?
Because every car’s mileage and operating life can be different, there are caveats surrounding after-market products. For example, they don’t offer a permanent fix with just one use. The makers of DIY additives for catalytic converters claim to have proven results in helping reduce harmful emissions by up to 60 per cent, but typically recommend using their product four times a year.
The DPF filter cleaners don’t have great feedback however, mainly because if the car’s own regeneration process isn’t doing the job or performing correctly, the build-up of deposits will only continue.
The Terraclean system is expensive but has excellent results, says Stuart Matthews of Carrevolution, a dealer based in Norfolk: “Any high mileage cars I sell get a Terraclean as it always improves driveability and emissions when they get an MOT”.
Some experts say the best way to reduce problems with an exhaust system in the first place is by using good quality, branded fuel, and to undertake longer trips on main roads, keeping the engine revs between 2,000 and 3,000rpm for between 30 minutes to an hour.