Petrol and diesel engines build up carbon deposits inside the cylinders over a period of time. This carbon build up happens for various reasons – from improper burning of fuel, to substandard fuel quality and general build up with age. It deposits itself as soot around exhaust valves, in the exhaust, on the cylinder head, on the piston and on the intake and exhaust manifold.
Over a period of time, especially in older cars, this carbon build up can lead to valves not closing properly, spark plugs fouling, exhaust sensors failing and other issues. Some of the first symptoms of carbon build up will include a lack of power and low mileage from the car. Severe cases will also show up as black soot deposits spilling out of the exhaust.
Carbon build up happens over a period of time. Usually the best time to decarbonize an engine is after it has done about 50,000km. This is a preventive maintenance procedure at this point and your vehicle wouldn’t have had too much carbon build up anyway.
Chemical decarbonisation involves running a chemical compound along with the fuel through the engine to breakdown carbon deposits. This then gets flushed out along with the exhaust gases. There are a couple of ways in which this is done. One way is to add the chemical along with some fuel in a separate unit that is connected to the fuel intake line on the car. The engine is started and the car is allowed to run for 15-20 minutes or until the mixture is fully utilized. This applies to both petrol and diesel engines.
This method of decarbonizing the engine is alright only as a preventive maintenance routine. Doing this every 50,000km or so will prevent carbon build up in the engine and keep it clean, increasing its life.
For engines that have severe carbon build up, a chemical decarbonisation won’t be quite effective. In this case, one will need to do a physical decarbonisation procedure. This involves opening up the cylinder head, removing the intake and exhaust valves and physically “scrapping” the carbon deposits off the valves, cylinder head and manifolds. The exhaust pipe will also need to be dismantled and cleaned thoroughly using high-pressure water. If the exhaust muffler is clogged with carbon deposits, sometimes it will need to be heated and tapped out, before flushing with water.
Periodic maintenance and preventive maintenance are ideal for a car, to keep its engine running clean and healthy for years. Is decarbonisation necessary? Yes, but only every 50,000 km or so. Don’t fall for the friendly service advisor’s advice at a service station that this is needed at every other service!