Engine Carbon Buildup: What it is, how to clean it and prevent it!

A new vehicle always comes with a clean engine with no contaminants. But over time, engine carbon buildup and soot deposits clogg the engine, this can happen rather quickly on modern vehicles. Coking occurs on its internal components and in the exhaust system, regardless of whether it is a diesel or a petrol engine. These deposits are called carbon deposits. Coking impedes the flow of fuel and leads to a loss of performance and higher fuel consumption. Nowadays it is necessary to clean the engine of your vehicle at regular intervals. This article will cover why carbon deposits form in the engine, which engines are prone to it and also how to prevent carbon buildups and how to clean those deposits if they do appear. Stay with us!

What is Engine Carbon buildup or deposits and why does it happen?

Engine carbon buildup or deposits are nothing more than a side product of fuel combustion in an engine. Carbon deposits are nothing more than a consequence of incomplete fuel combustion in an engine. The small percent of the fuel that does not combust in the combustion chamber evaporates and sticks to the inside of the engine.

Think of your engine as a wood burning oven, if the burning of the wood (fuel) is perfect, there is no smoke and no ashes, if the burning is incomplete, just like the burning of fuel in an engine is, there will be byproducts and one of those is carbon. Carbon soot deposits resemble the soot you find in a chimney of a house and the same thing happens in an engine, all the unburned fuel evaporates and sticks to the engine internals as carbon deposits. If these deposits build up it can cause serious engine problems.

Checkout this youtube video to see more examples of carbon build up in direct injection engines like the Volkswagen TSI.

Reasons for carbon buildup in an engine

  • Low quality fuel

Despites of what you might think, fuel is not nearly as good as it used to be years ago. It is much more contaminated and full of additives that do more harm than good, especially when it comes to perfect combustion. Fuel providers make more money, but your engine might suffer from the incomplete combustion of the low quality fuel.

  • Stop and go traffic

Stop and go traffic is a nightmare for you and your engine. The constant stopping and accelerating means that you are constantly filling your engine up with fuel that does not burn up completely. Try and apply the gas pedal calmly in order to not overfill your engine with fuel it does not need. Try avoiding stop-and-go traffic as well.

  • Short journeys

If your destination can be reached by foot or on a bike, then by all means, use your body. Drivers who use their cars for short journeys constantly, are experiencing much more problems with engine carbon build ups and deposits as those drivers who tend to drive their cars on longer journeys only. This is due to the fact that a cold engine will always be less optimal for complete fuel combustion. On shorter journeys your engine does not even have the time to warm up which leads to more and more carbon soot deposits.

  • Neglected car maintenance

Engine carbon buildup is more often in cars that do not get the attention they deserve. Having your engine oil changed in regular intervals is crucial for a healthy engine. When you take your car for an oil change, your mechanic might also detect and check if the engine has excessive carbon buildup in the engine based on the state of the oil. Do not neglect your maintenance schedule!

  • Slamming the throttle

Constantly abusing the gas pedal is a bad way to treat your engine. Your combustion chamber will be flooded with fuel that will not get burnt up entirely. Practicing a more linear acceleration technique can go a long way in engine health preservation.

  • Your engine is just more prone to carbon build up

Some engines are just more prone to carbon build ups than others, that is the harsh reality. These engines require regular carbon cleaning or checkups so it does not hurt to be aware of that. Continue reading to learn which engines exactly are more prone to carbon buildup.

Which engines are more prone to carbon buildup?

Modern direct fuel injection engines, both diesel and petrol are much more prone to carbon deposits in the engine than older engines with carburetors or port fuel injection systems.

Most modern turbo diesel and petrol engines are using a direct injection system. This means that the fuel injectors deploys fuel directly into the combustion chamber. This system has many benefits, a better fuel economy and less environmental pollution. However, these engines are more prone to carbon buildup than older engines that sprayed fuel into the intake port before it reached the combustion chamber.

Which parts of an engine pick up the most carbon deposits?

The most vulnerable parts of the engine are the fuel injectors and the intake valves.

Carbon that builds up on the tip of the fuel injector is the biggest nuisance. The tip of the fuel injector is incredibly precise and any kind of blockage will lead to symptoms like rough idling, misfires, increased emissions and poor fuel efficiency. Deposits on the fuel injector are more common with vehicles that only cover short distances. We analyzed all the problems you could also have with fuel injectors in this article.

Intake valves are prone to carbon buildups in a shorter time than fuel injectors. Carbon deposits stop them from opening and closing as they should which leads to a restricted air flow to the cylinder. This affects the engine power and fuel efficiency. A certain amount of carbon deposits is normal on all vehicles but carbon build ups are much more common and appear faster if the valve seals or guides are worn. Engines with variable valve timing in which certain intake valves stay open for longer are more prone to deposits of carbon particles. In older engines with port fuel injections the intake valves were regularly cleaned by fuel, but in engines with direct fuel injection this is not the case anymore.

Symptoms of built up carbon deposits in an engine

  • Weakened engine performance
    Be on the lookout for decreased acceleration, less power in higher gears.
  • Rough idling
    With a disrupted fuel injection or intake valve malfunction, your engine will not run smoothly as it should
  • Misfires on one or more cylinders
  • Error codes show up on diagnostic tools
  • Check engine warning light
  • Black smoke comes out of the exhaust when you accelerate
  • Knocking or pinging sound coming from the engine can indicate high levels of carbon buildup

How to prevent excessive carbon build ups in the engine?

Use only high quality fuel and approved fuel additives

Not buying the cheapest fuel will probably make the biggest difference. Certain fuel stations offer fuel with additives that promote complete combustion and in return less engine carbon build up. Certain car manufacturers also recommend using fuel additives that promote better combustion.

Maintain a regular service schedule

Regularly replacing your engine oil will make the biggest difference when it comes to carbon deposits. We cannot stress this enough! Your mechanic can also inspect the state of your intake valves when doing an oil change. High quality engine oils that are meant to be used on direct injection engines are designed with cleaning detergents that help clean up carbon deposits in the engine. Shorten the oil change interval if you take plenty of short journeys. Companies like Valvoline offer full synthetic engine oil that is made specifically for preventing engine carbon build up.

Have carbon buildup cleaned on a regular basis

Certain service centers and nowadays even car manufacturers of direct injection vehicles recommend implementing a carbon cleaning interval as part of mandatory maintenance. There are several ways of cleaning your engine which we will cover as we continue.

Take longer journeys on a regular basis

Longer highway journeys are a good thing for your engine. Any activity that keeps your engine running at high rpm’s for an extended period of time will help clean out any light carbon deposits. Take a trip somewhere every other weekend and help out your engine from all the short stop-and-go traffic journeys you endured over the week.

How to clean harmful carbon buildups in the engine?

There are several ways of cleaning carbon buildups in the engine, some can be done at home while others must be carried out with special equipment and the right supervisor.

Rev your engine up once in a while

Hitting those high RPMs is nothing to be afraid of, hit the highway and let your engine breathe a little, a few aggressive accelerations and a longer journey at highway speeds will ensure that your engine stays clean!

Use approved fuel additives

Certain fuel additives actually help your engine (most of them are junk) so if your car manufacturer or service center approves of any fuel additives that promote better fuel combustion, use them!

Visit a carbon cleaning professional shop

Since the introduction of direct fuel injection, carbon deposits have been a problem. So many professional service centers popped-up who use different methods to clean up the insides of an engine. Some use hydrogen, others use ultrasonic cleaning but they generally all do well. Make sure you choose a cleaning center with good reviews and expertise.

Regularly replace your spark plugs

Spark plugs that stay in your engine for an extended period of time, are a sure way to have poor fuel combustion. Replace your spark plugs at a recommended interval and ensure a good combustion rate!

Frequently asked questions

What is the cost of engine carbon build up removal and cleaning?

The cost of professional carbon build up cleaning ranges anywhere from 250$ to 1500$. The cost depends on the amount of built up carbon and the cleaning method used.

What are engine carbon build up symptoms?

Decreased engine performance, misfiring, rough idle are amongst the most common symptoms.

Where does carbon build up in your engine?

Mainly on the intake valves, cylinder heads and fuel injectors. Diesel engines also suffer from carbon deposits on the EGR valve and intake manifolds.

Do diesel engines get carbon build up?

Yes, modern direct injection diesel engines do get carbon build up. It is a common problem with diesel engines that make many short journeys.

Can carbon build up cause engine knock?

Yes, engine knocking and pinging are among the symptoms of built up carbon deposits.

How do I remove carbon build up from my engine?

You can use fuel additives, run the engines at higher RPMs for a longer period or take your car in for a professional cleaning.

What causes carbon build up in small engines?

The same thing that causes carbon build up in bigger engines, incomplete fuel combustion.


If you happen to have an engine with built up carbon deposits, do not panic! You are certainly not the only one and in most cases it takes a long time before there is real engine damage. If you suspect that the problems you are having with your car are related to carbon build ups in the engine, have your mechanic diagnose the problem and suggest a solution. In most cases, a fuel additive will resolve the issue. Even if you have to visit a professional cleaning center, the bill should not be enormous. 

Unfortunately, not all new technology comes without a set of new problems. Carbon build ups and deposits is something that most engine manufacturers are dealing with right now and we are constantly seeing new engineering solutions to this problem. Hopefully this will not be a thing we are worried about in the future!

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