What causes carbon build up in engines?

All internal combustion engines (ICE) no matter whether petrol, diesel, LPG, methane, hybrid, or any other hydrocarbon all create carbon build up as a natural product of burning fuel.

Book Your Carbon Clean Today
Which? Trusted Trader Logo

Reviews For our Carbon Cleaning Services

Ben Castle profile picture
Ben Castle
21:49 29 Apr 26
Highly recommend this company.

Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.

Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Adam Brown profile picture
Adam Brown
17:12 26 Apr 26
I rang Adrian after using him in the past and he got me booked in really quick, came out with constant updates on arrival time so didn’t have to sit around waiting. Did all the checks on the car then explained everything as it was being done, didn’t mind answering any questions asked. Mentioned a slight vibration and after it was all done the vibration was almost non existent sounded loads better and was driving in my opinion better. Really good job was very pleased and top man Thanks
Tim Ward profile picture
Tim Ward
07:49 25 Apr 26
All round a very impressive service.There is a noticeable improvement in my 100k mile diesel, it runs more smoothly and hopefully will have a better mpg.
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Lewis Jones profile picture
Lewis Jones
14:33 21 Apr 26
Cant be happier with the service on my 115k mile 2013 Hyundai i30 1.6CRDi (Diesel). Quick responses on email/whattsapp. Open communication on how their van/machine needs to be setup and how to prepare your car. The clean was quick and Adrian was highly informative in the diagnostics with whats normal and whats irregular (luckily nothing major was found). Also told me about how the cleaning process works which was interesting. After the clean (~50mins) the car has an increase in performance, throttle response, a smoother operating engine with less vibration and improvements in the mpg (~10mpg) which were all previous problems I had encountered. Could not recommend them enough as it now feels like brand new and will certainly be using them again when the time comes around (~25k miles later as suggested) or if I were to change car.
eddie affection profile picture
eddie affection
19:22 15 Apr 26
Very polite very knowledgeable communication excellent carbon cleaned two of my vehicles with excellent results picked up a fault with one (hole in intercooler ) which I never would have found I put problem right and all is now good fantastic serviceView more
English Kernigit profile picture
English Kernigit
12:20 09 Apr 26
Originally wanted a dpf clean but after speaking with Adrian, he recommended a carbon clean of my 2014 Mercedes sprinter. Turned up on time and with all the kit. Job done within the hour with some issues identified (new thermostat needed being chief). Almost immediately, my van runs smoother and quieter. Very happy with the results and equally with Adrian's no nonsense knowledge of the task and professionalism. Would definitely recommend you speak to him before anyone else.
Jamie Green profile picture
Jamie Green
19:41 07 Apr 26
Professional process with reassuring advice and feedback along the way. Definitely recommend Adrian to anyone.
Theo profile picture
Theo
18:20 05 Apr 26
From 55mpg to 72mpg! Perfect service couldn’t ask for more, the car runs smoother than ever, start to finish was given clear honest advice and help. Booked the carbon clean and diagnostic was kept in the loop with everything and given a detailed report of everything, really clear communication throughout. Would highly recommend.
Bidmond profile picture
Bidmond
21:13 04 Apr 26
5-star advice from Adrian at F5ECC. He provided some brilliant free advice and instead of just trying to sell me a service, he gave me some incredible technical insights for my Audi A3 that saved me from a costly and unnecessary repair. He clearly knows these diesel engines inside out and is a total professional who puts the customer first. When I eventually do need a carbon/DPF clean, he’ll be the only person I call. Highly recommended.
Carl Batute profile picture
Carl Batute
21:54 02 Apr 26
Adrian came to a carbon clean on 2 vehicles . Kia Sportage 1.6 crdi and a Mercedes A200 diesell 2.1. Kia was having no issues just was a regular clean as I have used Adrian for several vehicles and understand the benefits of a clean. Again I noticed better performance and start up. Mercedes had starting issues and inconsistent running. After the clean it was more responsive , noise from the exhaust valve seems to go a way and not present anymore . So a better running Mercedes also. To be clear the Mercedes when warm would bit and not restart so definitely improved performance and start up issues. Thank you . See you in the summer for the Renault Clio clean .
İlter Hayırsever profile picture
İlter Hayırsever
19:14 29 Mar 26
I had my 2016 Ford S‑Max 2.0 TDCi carbon cleaned, and the difference has been impressive. My average MPG has gone from around 41 to 45, which I honestly didn’t expect, but the improvement is real. The engine also feels a touch smoother on acceleration, especially when pulling away or overtaking.

Professional service, clear communication, and results that genuinely make a difference. Highly recommended.
Ionut Zorici profile picture
Ionut Zorici
20:15 28 Mar 26
Another great service from Adrian, helping me pass the MOT emissions test on my 21 yrs old MK5 VW Golf .Highly recommended his services including DPF cleaning etc .

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, carbon build up in the engine is minimal because combustion is clean and efficient.

Over time, this changes. In many vehicles, carbon build up can begin 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.

All internal combustion engines create carbon as a natural result of burning fuel. When combustion is not perfect, known as incomplete combustion, unwanted by-products are produced.

Book Your Carbon Clean Today
C8H18 + Air (mainly N2 + O2) → CO2 + H2O + CO + C  + NOx

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.

Note the ‘bad stuff’ in orange.

How carbon build up affects engine performance

As carbon build up gathers inside the engine, it 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
carbon build up

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.

Book Your Carbon Clean Today

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 increases vibration within the engine, placing extra strain on components. Over time, this can accelerate wear on:

  • Fuel injectors
  • Engine mounts
  • Clutches and flywheels
Book Your Carbon Clean Today

Where carbon build up collects

Carbon deposits commonly gather in components such as:

  • EGR valves and EGR systems
  • Inlet manifolds
  • Intake ports and valves

These restrictions further reduce airflow, making the problem worse and accelerating carbon build-up.

carbon build up

Why is carbon build up 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.

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 buildup in petrol and diesel engines far more common.

Book Your Carbon Clean Today
What causes carbon build up in engine

Why carbon build up cleaning matters

Once carbon build up starts, combustion becomes less efficient, emissions rise, and deposits accumulate faster. Without carbon build up cleaning, this cycle continues, increasing the risk of EGR faults, inlet manifold blockages, DPF issues, and long-term engine wear.

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

The good news…

Regular engine carbon build-up cleaning can help break this cycle, restoring smoother running, improving efficiency, and reducing emissions. Thankfully, this is something we can help with.

F5ECC Team
Book Your Carbon Clean Today