Engine decarbonisation: When do you need this done?

One of the things you will hear almost every service station try to sell you is “engine decarbonisation”. But do you really need this?

CarToq tells you when exactly you would need this service and when to refuse it.

Engine decarbonisation: When do you need this done?
Photo: Don’t fall for the friendly service advisor’s advice at a service station!

What is decarbonisation?

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. Also read: Seven lies car dealers will tell you!

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.

Service stations, though, would try and sell you this service even if your vehicle has done just about 20,000 km – because it’s a money spinning venture for them. Service stations charge anywhere between Rs. 1,500 to Rs. 2,500 for this service depending on the car brand. This charge is for a “chemical decarbonisation” procedure.

There are two ways in which an engine can be decarbonized – Chemical decarbonisation and physical decarbonisation. There are other “home-remedies” as well. Also read: A guide to car engine oils

Chemical decarbonisation

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. Also see: 10 spares and tools to carry in your car, always!

Physical decarbonisation

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.

This decarbonisation procedure is expensive as it involves higher labor costs.  Such a procedure could cost anywhere between Rs. 3000 to Rs. 5000 depending on the car brand and the workshop doing the process.

Home remedies

There are some home remedies that you could use to keep your engine in good health and prevent carbon build up. Using a fuel-system additive with the fuel once every two months will help in keeping the engine clean. Brands such as Valvoline, STP, Wurth and other sell products that blend with either petrol or diesel and help remove sludge and carbon deposits.

Another old trick in the book with older carburettor driven cars as well as older diesel engines was to decarbonize the engine using a fine water mist. This involved removing the air filter and spraying a fine mist of water using a household spray bottle over the intake while the engine was running and being revved. The water would form steam in the cylinders and resort to a sort of “steam cleaning” of the engine. This process is dangerous as it can ruin an engine if done improperly – leading the engine to seize up! We don’t recommend this process ideally.

You may also want to check out these stories:

10 quick weekly checks for your car


Choosing the right tyre: How to choose


Car troubleshooting: What to do when gears are hard to shift

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!

Share your experience with engine decarbonisation with the CarToq community.