DIY – Top-Engine Cleaning (Decarbonization)


August 27, 2013 by quirkyuncle

As they age, all engines get dirty on the inside throughout the combustion path (from the air intake to the exhaust). Using a top engine cleaner, such as SeaFoam Spray, helps remove the gum, varnish and other deposits that build up inside these areas of your engine over time. A cleaner engine is a happier engine that will perform better and give you less problems.

SeaFoam Can

Cleaning out your engine will help it run better, improve it’s fuel economy, and help extend the life of engine components. Using a top engine cleaner can help:

  • Reduce stalling, hesitation, and pinging
  • Make your engine idle smoother.
  • Improve your exhaust emissions and gas mileage.
  • Clean carbon deposits from inside the engine (decarbonize).
  • Clean the intake valves and pistons.
  • Clean the throttle body (a little).
  • Clean the catalytic converter (a little) and reduce catalytic converter odors.
  • Restore lost engine power.

Note: There is no such thing as a miracle cure: using a top engine cleaner won’t make you better looking or prevent the zombie apocalypse. That being said, I have used top engine cleaner several times over the years on a number of vehicles and have noticed that they all run better afterward. Cleaning the engine won’t fix a broken or worn out part, but will optimize whatever you have. It’s kinda like mouthwash for your car: it won’t fix a cavity, but sure makes your breath smell better.

The following procedure shows using SeaFoam Spray top engine cleaner on a 2000 Ford Mustang V6. There are several other brands of top engine cleaner available and all are used in a similar manner. Whichever brand of top engine cleaner that you buy, follow the instructions that come with the product! Instructions for using SeaFoam Spray are on the can and also appear on the SeaFoam website (click here to see the instructions).

SeaFoam Spray is applied to the intake system, immediately before the throttle body, using an applicator tube that comes with the spray can. Performing this procedure on the Mustang was very easy, since the throttle body is easily accessible. Other vehicles might not be as simple. Look and see before you get started!

Tools: Screwdriver or nut driver to fit the hose clamp on the intake air duct (shown below)
Time: 60 minutes
Difficulty: Easy (provided your throttle body is easily accessible)

You can order SeaFoam Spray from

Note: Doing a top engine cleaning can generate a lot of smoke. As with any procedure where you run the engine, it must be performed outdoors. In this case, you also need to pay attention to wind direction, so you don’t fill your house with smoke or anger your neighbors.

Let’s get cleaning!

To perform a top engine cleaning, complete the following steps:

  1. Top engine cleaner is injected at the input side of the throttle body. Locate the throttle body on your car. To find it. follow the intake air duct from the air filter to the intake manifold. The throttle body is typically bolted to the intake manifold with the intake air duct secured to the throttle body using a large hose clamp.

    Locate throttle body

  2. Loosen the hose clamp screw that holds the intake air duct to the throttle body.

    Loosen hose clamp

  3. Remove the intake air duct from the throttle body. It might be stuck in place. Rotate the air duct slightly back and forth to break the seal. You will need to pull firmly on the intake air duct to work it off of the throttle body and remove it.

    Remove air duct

  4. Carefully measure the distance from the front edge of the throttle body to the closed throttle plate that is inside. This distance is needed to correctly set up the Seafoam Spray tubing.

    You can measure the distance by inserting the end of the SeaFoam Spray applicator tube gently into the throttle body along one edge until it stops and seeing how far it goes in. In most cases, if you insert more than an inch or two of the applicator tube into the throttle body, something is wrong. Pull the applicator tube out and try at another location around the inside of the throttle body perimeter.

  5. Install the hook guide on the SeaFoam Spray applicator tube (red). The end of the applicator tube needs to be set so that when it is hooked over the front edge of the throttle body, the tip of the applicator tube is approximately 1/4-inch from the closed throttle plate.

    Install SeaFoam Spray tube

  6. Insert SeaFoam Spray applicator tube and hook guide into the front edge of the throttle body. Make sure that the applicator tube does not slip from its position in the hook guide during assembly. If the applicator tube moves, disassemble and reset the applicator tube to the correct length.

    Insert SeaFoam Spray tube in throttle body

  7. Replace the intake air duct on the throttle body and secure it with the hose clamp. Make sure that the SeaFoam Spray applicator tube and the hook guide do not shift during assembly.

    Replace air duct

  8. Connect the can of SeaFoam Spray to the other end of the applicator tube.

    You are now ready to spray!

    Ready to spray

    Note: You will need to maintain a constant engine RPM while spraying SeaFoam Spray into your engine. The SeaFoam will cause your engine speed to fluctuate, so constant adjustments the throttle will need to be made.

    • If your throttle body is controlled by a mechanical linkage, you can perform the throttle adjustment with one hand while you spray with the other hand.
    • If your throttle body is electrically controlled, you will need to have an assistant sit in the car and perform the throttle adjustments using the gas pedal.

    To determine which type of linkage your car has, have an assistant press the gas pedal while you look for movement on the outside of the throttle body. This movement indicates presence of a mechanical linkage and where you need to press to adjust the engine speed. The mechanical throttle linkage, and where to press, for a 2000 Ford Mustang V6 is shown below.

    Locate throttle body

  9. Place the car in park or neutral and set the parking brake. Start the engine.
  10. Increase engine speed to between 500 and 1000 RPM above the normal idle speed. This RPM increase is required so that the chemicals are properly dispersed.
    • If your car has a tachometer, use it to read the engine RPMs.
    • If you have a OBD reader, use it to read the engine RPMs. (If you have a BlueDriver Scan Tool, you can read the engine RPMs using your smartphone or tablet.)
    • If you have no means of measuring the engine speed, you will need to estimate the RPMs by sound. Most engines idle between 750 and 1000 RPM. If you raise the pitch of the engine so its frequency is twice that heard at the normal idle speed, you should be OK. (If this makes no sense to you, STOP and ask for help.)
  11. Spray the SeaFoam Spray while holding the engine RPM constant. A full application of SeaFoam Spray will take several minutes.

    You can either use half the can or the full can. I used a full can, as the car was running quite rough before I started.

  12. When you are done spraying the SeaFoam Spray, release the throttle and allow the engine to return to its normal idle speed; then, shut off the engine.
  13. Loosen the hose clamp and remove the air duct from the throttle body; then, remove the SeaFoam Spray applicator tube and hook guide from the throttle body.
  14. Install the air duct on the throttle body and secure it by tightening the hose clamp.
  15. After the car has sat for about 5 minutes (from the time when it was turned off), restart it. The car will likely run rough and smoke a lot for a few minutes.
  16. Take the car for a ride and drive it aggressively (obey all laws and be safe!). Additional grime inside the engine will be cleaned up during the first several miles of normal driving.

The top engine cleaning process is now complete!

You should note an improvement in how the car runs after you’ve driven it for a few miles. If the car still runs bad, you can repeat the top engine cleaning process; however, I would investigate if other problems might exist before doing so.

If you have an OBD code reader, you can check for trouble codes that have been detected but have not yet triggered the check engine light (see the DIY – Help! My “Check engine” light is on! for more information).

I’ll cover more engine diagnostic and cleaning techniques in a later posting. Check back soon.


  1. Skip Ayers says:

    Is there any need to do an engine oil change after the decarbonization?

    • says:

      No, you do not need to perform an oil change after decarbonization. The process takes place in the in the intake, combustion chambers, and exhaust and does not affect the oil.

  2. Charles says:

    Can ABRO carb & choke cleaner be used

    • says:

      Carb and choke cleaner will clean the intake side. Not sure if it will do much good inside the cylinders and exhaust. It depends on what you are trying to clean.

      It is worth noting that “carb/choke cleaner” can be stronger than “throttle body cleaner.” Use the correct cleaner for your intake configuration to prevent damage. To clean a very dirty throttle body, use the cleaner and scrub gently with a nylon toothbrush, wiping the grit away afterward with a paper towel. Try not to soak the area around the shaft a lot, as the cleaner will remove the lubricants from the bushings that support the throttle plate shaft.

  3. Pat says:

    Can I use this can on a 2003 Tiburon V6 engine? Cause I noticed the can says only 2 and 4 cylinders…

    • says:

      It says 2-cycle and 4-cycle gasoline engines. It does not matter how many cylinders.

      Most gasoline engines in cars are 4-cycle (also called 4-stroke). 2-cycle (also called 2-stroke) engines are found in power equipment (chainsaws, weed trimmers, blowers) and some motorcycles, where a gasoline/oil mixture is used.

      Diesel engines are also 2-cycle, but I do not think SeaFoam is designed for use with diesel engines. I believe they have other products for diesel.

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