What causes carbon build-up in engines?

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.

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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engine carbon build up
engine carbon buildup
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Brad G profile picture
Brad G
21 hours 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 profile picture
Robert Bedford
3 days ago
Great ppl full of advice and very helpful quick to reply definitely use again thanks guys
Graham Ward profile picture
Graham Ward
4 days 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 profile picture
Kimberley Everest
4 weeks 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 profile picture
Gary Simpson
1 month 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.
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Emils Matulis
1 month 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 profile picture
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
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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
Emma Valentine profile picture
Emma Valentine
2 months ago
Couldn’t ask for better service. Had a carbon clean done this week on my partner’s Astra. Adrian responded very quickly to my initial query and got us booked in for the next day. He was very thorough and explained everything that I wasn’t sure of (my knowledge on cars is awful). He provided the fault codes and the live engine data and gave great advice about how to fix the current issue we were having with our car. The car runs very smoothly and is finally lovely to drive again, wish we’d done this sooner. He was very friendly & polite which put any worries I had at rest. I wouldn’t go anywhere else. Thank you so much!
Seagrave Media profile picture
Seagrave Media
2 months ago
"I recently had F5 Engine Carbon Clean work on my three vehicles—a 2012 BMW X1, 2007 Jaguar XJ, and 2005 Audi TT—and the results are superb.
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
Andrew Bailey profile picture
Andrew Bailey
2 months ago
Highly recommend!!
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Charlie Stokes profile picture
Charlie Stokes
2 months ago
Steve came out to give our DPF a full clean on our bmw 2 series the before and after results are incredible. More power better MPG and overall the car feels way better to drive. He showed us the before and after statistics. We are definitely getting him back to do a carbon clean

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  + 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.

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
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.

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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
carbon build-up fuel injectors
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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 a build up of carbon.

carbon build up

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.

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.

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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 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 cleaning can help break this cycle, restoring smoother running, improving efficiency, and reducing emissions. Thankfully, this is something we can help with.

F5ECC Team
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