What causes carbon build-up in engines?

When an engine is new, it runs smoothly and quietly, delivers good fuel economy, and produces low emissions.

All internal combustion engines (ICE) no matter whether petrol, diesel, LPG, hybrid, methane, or any other hydrocarbon all create carbon build up as a natural product of burning fuel. This gather over time affecting performance, combustion efficiency and if left long enough component wear/failure.

In this article we will discuss the background, a little bit of the science, some of the knock-on effects of not dealing with it and how we can help to minimise the issue.

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Reviews For our Carbon Cleaning

Mohammad Hossen

3 days ago

Fantastic service from Leon- what a knowledgeable gentleman who did a thorough check and diagnostic and advised accordingly on key issues. Car run beautifully following the carbon engine clean.

michael mcneive

5 days ago

I had a DPF clean which has worked perfectly and got my diesel Rav4 back into perfect driving condition. Steve, the technician was very friendly and talked me through the whole diagnosis and treatment.

Silent Scream

6 days ago

Recently bought a Mazda cx5 diesel and wanted piece of mind the engine had been cleaned. I was getting at most 44mpg (best I had got) I am now getting 49mpg. Well worth it and great people. Thanks again !

Alan Moore

1 week ago

Just had my car done by F5ECC. Adrian talked me though how the process works. This is the second Merc I have had done by him in 2020. C250cdi and now a C350e sport. Noticed straight away more mpg. The car felt a lot smoother on acceleration. I was quite shocked at how much quicker and responsive the car was when I put it in sport+. I highly recomend having this done. Alan Moore. 66 plate C350e 75000 miles.

JAKE tyler

1 week ago

Adrian was very friendly and professional, showed me everything he did and talked me through the process… Plus car feels great 10/10 would recommend

Owen Moore

2 weeks ago

Adrian came out and did a carbon clean on my Mercedes CLA45. If you've purchased a used car that's done a good amount of miles then I would highly recommend getting this done. It made all the difference to mine. Throttle response is better the car feels better as it climbs through the gears. Adrian was here for about an hour, was happy to talk through the process and shared diagnostic info straight to my phone. Really helpful and knowledgeable. Owen Moore.

Paul Auton

2 weeks ago

Had Adrian carbon cleaning my Audi 2021 A4 tdi .waited to see results over a period of time .car runs smoothly and accelerates with ease The car seems to get to 60 mpg very quickly and just goes up from there so impressed. Adrian Improved the 4 injectors performance but found no 3 slightly out of spec .Adrian went tho the cars diagnosis system very impressive I would highly recommend paul .thanks Adrian

Sanjeev Kumar

3 weeks ago

I found this organisation on Google. It had great reviews and the service which I required which was a carbon clean. I found Adrian very helpful and knowledgeable. While he was carrying out the service he explained everything to me and how it works. The car feels better now with it being more responsive and quieter. I would recommend Adrian and his company to friends and family if they required his services. Thanks Adrian hopefully see you again sometime.

Robert Maybury

3 weeks ago

This was my first experience with F5 carbon and DPF clean. I was a little desperate as I had been let down twice by a larger franchise company. Mark the technician managed to fit me in at short notice, what a stroke of luck for me I found Mark to be an extremely knowledgeable and professional guy. After running the diagnostic and clearing a few issues he managed to get my DPF working properly and able to do the regeneration process on its own so only charged for the diagnostic even though I had booked for a full DPF cleaning. I cannot recommend F5 enough it's a real pleasure to deal with them. All round excellent service. Thank you guys.

Owen Simpson

2 months ago

Adrian is a lovely fella, explained the process, carried it out well, clearly done exactly what it needed to do as I blew a load of stuff out the back when I drove it after. Will definitely be coming back in the future.

kenny bennet

2 months ago

Great job Car running a lot better Highly recommend

Iain Tribick

2 months ago

Steve arrived to give my Jaguar xfs an engine carbon clean. Presently on 107,000 miles. Explained the process and was obviously very knowledgeable about the process and expected outcomes. And he was a thoroughly nice chap. The V6 in the xfs is a quiet, smooth, powerful unit and I was not sure of what improvements I would get. Well, I’m impressed. The power delivery is smoother, the engine even quieter and 6 mpg better to boot. If you want to do one thing to maintain and improve your motor, then this is what you should do.

Where does carbon build up come from?

When an engine is new, it typically runs smoothly and quietly, delivers good fuel economy, and produces low emissions. At this stage, the effect of carbon building up in the engine is minimal because combustion is cleaner and efficient whilst components are new.

Over time, this changes. In many vehicles, carbon build up can begin to affect smooth running as early as 10,000 miles, particularly in modern petrol and diesel engines that rely on complex emissions control systems and are often used for short journeys.

The combustion process is not perfect, known as incomplete combustion and the dirtier the engine gets the worse it gets – more unwanted by-products are produced.

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C₈H₁₈ + Air (mainly N₂ + O₂) → CO₂ + H₂O + CO + C + NO_x

This is an example of incomplete combustion of octane.

Alongside carbon dioxide and water, it produces carbon monoxide, solid carbon particles (soot), and nitrogen oxides.

The ratio of these by-products varies depending on driving style, engine condition, fuel quality, and temperature.

All internal combustion engines (ICE) create carbon as a natural result of burning fuel.

Note the ‘bad stuff’ in orange.

How carbon build up affects engine performance

As carbon build up gathers inside the engine, it gathers on surfaces, sensors, injector tips and interferes with normal airflow and fuel delivery. The engine gradually loses the smooth, balanced running it once had and may begin to feel lumpy, uneven, or sluggish.

To compensate, the engine injects more fuel just to keep running. This is known as running rich. As this continues:

Fuel economy drops
The engine becomes noisier
Performance feels less responsive

This cycle explains what causes carbon build-up in an engine to get worse over time. Dirty combustion creates more deposits, which then create even dirtier combustion.

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Emissions & MOT failures

When an engine runs rich, carbon build up causes higher emissions. Levels of carbon monoxide and carbon particles increase, which can eventually result in an MOT emissions failure.

This is especially common with carbon build up in diesel engines, where soot forms more readily due to the way diesel fuel burns.

Wear & component damage

Carbon buildup does not only affect emissions. Uneven combustion and increased friction and vibration within the engine places extra strain on components. Over time, this can accelerate wear on:

Fuel injectors
Engine mounts
Clutches and flywheels

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Where carbon build up collects

To reduce emissions, modern vehicles are designed to trap and reuse exhaust gases rather than release them. Systems such as EGR valves, DPFs, catalytic converters and GPFs prioritise keeping soot within the vehicle. While this benefits the environment, it also makes carbon build-up in petrol and diesel engines far more common in areas such as:

Catalytic Converters
Combustion Chamber
EGR valves and EGR systems
Injector Tips
Pistons and Cylinders
Inlet manifolds
Intake ports and valves
Turbo Vanes

These restrictions cause vibration, sluggishness, over-fuelling and further reduce airflow, making the problem worse and accelerating a build up of carbon.

Even with cleaner fuels and modern additives, carbon build up does not disappear completely. Modern engines simply create the conditions for it to form.

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Why is Engine carbon more of a problem now?

Older engines were far simpler. Most unwanted combustion by-products were expelled directly through the exhaust, so carbon build up inside the engine was less noticeable.

Why carbon build up cleaning matters

Once carbon build up starts, combustion becomes less efficient, emissions rise, and deposits accumulate faster.

Without carbon cleaning, this cycle continues, increasing the risk of EGR faults, inlet manifold blockages, DPF issues, and long-term engine wear.

The good news…

Regular engine carbon cleaning can help break this cycle, restoring smoother running, improving efficiency, and reducing emissions.

Thankfully, this is something we can help with.

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What causes carbon build-up in engines?

Reviews For our Carbon Cleaning

Where does carbon build up come from?

C8H18 + Air (mainly N2 + O2) → CO2 + H2O + CO + C + NOx

How carbon build up affects engine performance

Emissions & MOT failures

Wear & component damage

Where carbon build up collects

Why is Engine carbon more of a problem now?

Why carbon build up cleaning matters

The good news…

C₈H₁₈ + Air (mainly N₂ + O₂) → CO₂ + H₂O + CO + C + NO_x