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

Mircea Marius Popa

1 day ago

Had the pleasure to meet Adrian this morning who performed a carbon clean on my bmw 525d
Very knowledgeable guy, I was really impressed.
Car drives much better now, highly recommend.

Thanks Adrian

Marius Popa

Mark Woolley

5 days ago

Adrian went above and beyond at every stage. Couldn’t recommend Adrian as a person and the service highly enough.

william farrell

1 week ago

had my jaguar xf sportsbreak car engine cleaned and omg its like new what a great job the power is back Engine diagnostic was brilliant and the service was so good. I would recommend it to anybody.

Tracey Jane King

1 week ago

Leon came out to my car about a month ago. He was brilliant, he did some diagnostics, asked some questions and then got to work sorting out my problem. He was extremely thorough and I could tell he genuinely cares about providing a first class service. Fantastic!

Brad G

3 weeks ago

Iv had the pleasure of having 2 Carbon cleans from both Adrian and Mark. Both lovely gentlemen and you can tell they love what they do. My car failed on emissions and this helped me get the car through the test, and at the time, I REALLY needed a pass because I couldn’t get anywhere. These guys saved me. Not only that, it’s a lot cheaper here compared to other places also. Thank you so much and look forward to seeing you in future endeavours.

Robert Bedford

3 weeks ago

Great ppl full of advice and very helpful quick to reply definitely use again thanks guys

Graham Ward

3 weeks ago

First class service, very professional and nice guys.
Very knowledgeable on issues with electrical problems with my car.
Arrived on time and completed the work as you would expect from a good reliable company.

Kimberley Everest

1 month ago

What a great experience with Steve today! From start to finish went through the diagnostics step by step with me, explaining everything in detail! Flushed and cleaned the dpf for me cannot fault him at all, work done at ur front doorstep would definitely recommend Thankyou so much for all your help!

Gary Simpson

2 months ago

Today Adrian from F5 Carbon7 DPF Clean came to de carbonise my xc60 he arrived bang on time he was very courteous and explained in great detail what the process was .
He set up within 5 minutes and went on to the diagnostics and talked me through what was coming up after a reset all was clear. It took about 1 hour in total great job well happy would definitely recommend Adrian well mannered gentleman.

Emils Matulis

2 months ago

Called for one service, but gentlemen helped diagnose the real problem and as well explain how to fix it!

Leon has great knowledge! Would recommend!
Will use in future!

Caroline Muscroft

2 months ago

Weve gone away to scarbrough on holiday and my dpf was blocked and not running properly. Messaged and came out to us the next day! Brilliant service thankyou so much! Will be booking in for the carbon clean next

Craig Harmieson

2 months ago

Amazing service, didnt expect too much but totally blew mind, performance was increased, not much but I'd recently had a new turbo, so didnt expect much, as for mpg, I was expecting afew mpg here or there, but in truth it blew my mind, I have a 2005 mondeo st estate with 162k on the clock, and it went from 45.4 mpg on motorways to 68.8, posted video as proof, should highly recommend

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