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Removing Carbon Buildup

Every time a gasoline engine runs, carbon deposits form on the piston crown, combustion chamber (CCD), and intake valve (IVD). Engine performance and starting suffer.


A buildup of carbon on the IVD impacts airflow into the cylinder, and it can leach into the fuel. Carbon in the CCD also absorbs fuel and heat, making the engine more prone to knock or ping under load.

Using water is not very effective
A technique that old-time mechanics would employ is to drip water or automatic transmission fluid into the engine’s induction system to try and break the deposits loose. This was not a good procedure. A number of companies developed a drip tool and chemical that would safely and easily remove buildup from both the IVD and the CCD.

That tool is essentially a bottle that holds the chemical, a flow valve, and a vacuum hose to connect to the engine. When used with the proper agent, it does an outstanding job of eradicating carbon deposits in an engine.

Smaller engines do not have a vacuum port to attach a drip tool. In this case, you need to use a piston soak chemical through the spark plug hole(s). A good chemical is General Motors’ Upper Engine and Fuel Injector Cleaner. After that, run three to four tankfuls of gas treated with a product such as Chevron Techron Fuel System Cleaner. The GM product attacks the CCD, and the enhanced gasoline will impact both IVD and CCD.

Of course, it’s best to never let carbon form. A regimen of good-quality gasoline combined with the use of a product in the fuel tank a few times a year will keep carbon at bay and the engine humming.

Top image: The valve on the right is laden with carbon. For the cleaner to attack and remove this deposit, it must be introduced via the induction system.

Right-top: The drip tool houses the chemical and is drawn to the induction system by engine vacuum.





General Motors sells a chemical called Upper Engine and Fuel Injector Cleaner (part number 88861802) for carbon removal that is excellent for use in a drip tool and as a soak on the piston.

To soak a piston, pour 2 ounces in each bore and let it sit overnight. Then turn the engine over by hand to push out the cleaner. Be sure to change the engine oil (it will leak past the rings). Start and run the engine under load. It will smoke until the chemical is burned off. The longer it smokes, the more carbon there was.

With the drip tool, the engine should run around 1,500 rpm for 30 to 45 minutes. Adjust the flow for around one drip per second. The high speed is used to carry the chemical into the cylinders and to not allow it to puddle in the intake manifold.

Right-bottom: Better tools provide a sight glass with a flow restrictor so you don’t accidentally hydro-lock the engine by passing too much liquid. Always follow the manufacturer’s guide for each tool. When done, put the engine under load for a few minutes to burn off the loosened carbon.

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