Carbon cleaning can remove sooty carbon deposits from your engine

A well-maintained modern car should be capable of covering six-figure mileages without needing any major attention. But it is reasonable to expect some drop off in performance as a car gets older and components wear.

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Many garages will recommend carbon cleaning as a way of restoring some of that lost performance, or as a way of helping your car pass the emissions part of the MoT test. But what is engine carbon cleaning, and does it work? Is it just expensive ‘snake oil’ or can it bring tangible benefits to your car?

Why might you need your engine carbon cleaned?

First, let’s look at the reasons an engine might need to be cleared of carbon at all. Petrols and diesels produce power by burning fuel, and this creates sooty exhaust gases. Emissions control devices such as catalysts and diesel particulate filters keep the amount of soot which reaches the atmosphere to a minimum, but there is still some which is deposited on components inside the engine and exhaust system. 

Vintage cars built before modern oils and fuel technology came about would need a ‘decoke’ every few thousand miles, which involved opening up the engine and physically scraping off the carbon deposits. Thankfully that is no longer the case, but engines can still require a carbon clean - especially (and ironically) those which are fitted with advanced emissions control equipment.

Petrol cars are usually less susceptible to ‘coking up’, as the fuel is actually quite good at cleaning the components as it passes through. However, many modern engines use Gasoline Direct Injection to improve efficiency where petrol is squirted directly into the combustion chamber and doesn’t get passed over as many parts. This means some GDI engines have a reputation for becoming clogged.

Diesels are even more affected, as the fuel itself doesn’t burn as cleanly. The exhaust gases are often fed back into the combustion chamber to be burned again and this movement of sooty fumes is bound to result in a build-up of deposits over time. Once the fumes are finally expelled from the engine they still have to pass through a particulate filter and a catalyst. These too can become clogged with carbon deposits.

Different types of engine carbon cleaning

Why you could consider engine carbon cleaning. There are several different services which are offered, either by mobile operators or a network of garages who have bought the equipment. 

The method involves a technician tapping into the fuel system and injecting Hydrogen ( Hydro, HHO ) into the engine. This makes it burns hotter and in the same time hydrogen dissolves carbon to a fine dust called hydrocarbons and cleans the components, everything goes out safely through the exhaust. Owners who have had the treatment say there is visible soot being expelled from the exhaust after the treatment, suggesting that it is having effect. 

The other method is more traditional and invasive, between £1000 -£2500. It is simply removing components from the engine and cleaning them, either with solvents or by ‘blasting’. This is a specialist job, and often crushed walnut shells are used as the abrasive as they are hard enough to remove carbon but won’t harm the engine components.