Carbon buildup on pistons. Causes and solutions

Carbon buildups are a common cause in the engine that has both a natural cause due to the wear of the engine parts over time and causes related, in particular, to the use of poor quality oil or poor quality fuel.

So, it’s better always to check for these soot deposits even if the engine is new to prevent other bigger issues in the future.

Carbon buildups in the engine and coking are the top reasons why engines fail, so you should not neglect this problem.

What are the causes of carbon buildup in cylinders?

The main reason why carbon deposits form in the engine cylinder is the combustion of low-quality fuel mixed with the burning of leaking oil from under the piston rings or valve stem seals. This happens because:

  • You use excessive additives and low-quality additives both in oil and fuel;
  • You use low-quality fuel
  • The car runs with an increased engine heat regime;
  • You drive very short distances;
  • Oil change lines are damaged;

Whether you have a diesel or a petrol car, carbon formation in combination with general wear affects eh engine’s life, although engines that run on LPG are less prone to this damage because LPG is the cleanest fuel.

Deposits formed on different parts of the piston pose the greatest danger to the engine. But also buildups on valves are a big problem. Carbon deposits can absorb fuel, resulting in an improper fuel-air mixture, engine detonation, and, of course, serious damage.

Soot on the side surface of the piston and the compression rings accelerates the wear of the cylinder. Coking of the oil removers clogs the oil drainage channels and this not only contributes to damage to the cylinder but also disrupts the operation of the oil system as a whole.

First, deposits will deprive the rings of mobility, thereby reducing compression, and leading to oil consumption. If the gap between the piston groove and the ring completely disappears, then the pressure on the cylinder walls increases, and the liners will wear.

Carbon buildup on piston rings

Deposits on the rings reduce the amplitude of the oscillatory movements of the rings. As a result, the piston group will wear out and the compression in the cylinders will drop. Over time, the rings become filled with deposits, which will drastically reduce their normal operation.


If buildups are formed on the piston rings you will often notice:

  • a decrease in engine power;
  • a bad start;
  • poor response when you press the gas pedal;
  • increased fuel consumption;
  • blue smoke from the exhaust;

It’s recommended to start cleaning the pistons and the piston rings when you see that the car has an increased oil consumption that often causes blue smoke from the exhaust.

Also, clean the pistons if you have low compression in the cylinders. To see if the compression is good, you can measure it with a special cylinder compression tester.

You need to know that if the wear of the piston parts is high, then cleaning the deposits is almost useless, you have to replace the whole piston.

Carbon buildup on the piston crown

Direct contact between fuel and high-temperature surfaces is responsible for deposit formation. The resulting carbon deposits cover the walls of the combustion chamber and interfere with heat removal from the cylinder parts.

This will lead to greater damage such as a burnout valve and a bent piston, a premature ignition of the fuel mixture, leading to a change in geometry and destruction of the piston.

Also, buildups can cause detonation leading to engine power loss.

How to remove carbon buildup from pistons and cylinders

There are some methods you can use to get rid of formed deposits on pistons.

You can do an engine flush, which requires the engine to be removed and washed with a solvent by well-trained personnel. This method has a high rate of success, but if the person does not do this properly and makes mistakes, this could mean trouble for the engine.

Also, there is an option to add special additives that are added in the fuel that clean deposits from various parts of the engine, and then the deposits are eliminated through the exhaust. But this method is not that effective.

You can opt for engine de-carbonization. This new method is said to help to get rid of carbon deposits, clean the whole engine even the O2 sensor and the catalytic converter from deposits, and enhance the engine performance by reducing noise and vibration and restoring fuel efficiency. However, this method does not guarantee success.

A large variety of engine decarbonization tests showed that the engine did not have a “spike” in performance, other tests showed that the car did not increase at all the engine performances, so this method has not proven well in removing deposits or increasing engine performance.

When should you clean the engine and pistons from carbon deposits?

As a general rule, if the engine is new and you maintained it properly, you can check it at 90.000 – 100.000 km (56.000 – 62.000 miles) but if you used low-quality fuel and low-quality oil, chances are that deposits formed earlier.


Carbon buildups are a natural cause and their premature appearance is caused by poor engine maintenance. Using high-quality engine oil and fuel helps to reduce this to happen faster than it should.

When you do have to perform a cleaning from carbon deposits, it’s always best to go to a specialized workshop with qualified personnel that removes the engines and does a great job in cleaning the engine and its parts from carbon buildup.

Scroll to Top