Sticking Valves From Carbon Deposits – What Should You Do

Sticking Valves From Carbon Deposits - What Should You Do
Sticking Valves From Carbon Deposits - What Should You Do

The first sign of sticking valves is usually engine missing or running rough when cold.

Sticking valves can also simply be the byproduct of cold-weather operation.

In this case, the sticking valves will often work free as the engine warms up.

Doing a cylinder leak down test when cold may confirm sticking valves.

Sticking valves can also be a sign that there are carbon deposits on the valves.

Carbon deposits can form on your valves for a few reasons.

Often, carbon deposits are the result of a rich fuel mixture. It can also be the result of oil passing through a worn valve guide. Oil is pulled through the intake valve guide and into the combustion chamber, where it’s burned. On the exhaust side, a worn valve guide can allow oil to sit on the valve and form deposits.

A loss of compression, poor combustion or cold-engine operation can also cause deposits to form on the exhaust valves.

Extremely worn valve guides can also result in sticking valves. They are more likely to manifest as engine misfire or spark plug fouling before sticking.

Numerous cold starts and warm-up cycles, excessive idling, short trips and around-town motoring are all ideal conditions for rapidly forming carbon deposits.

Bent Valves
Bent Valves

Bent Valves

The most common failure of valves is bending as a result of contact with the pistons. The valves contacting the top of a piston is due to incorrect engine synchronization.

Possible causes of bent valves are:

  • Sticking Valves From Carbon Build Up.
  • Timing Chain/Belt Breakage.
  • Incorrect Installation Of New Belts and Chains.
  • Weak Or Broken Valve Springs.
  • Engine Overheating.

If you suspect your engine may have bent valves, it is crucial not to attempt to start the engine.

Burnt Valve
Burnt Valve

Burnt Valves

The other common type of valve failure is burnt valves. Essentially this is caused by combustion gases escaping between the valve and valve seat when they are not sealing correctly. Normally this type of failure affects the exhaust valves only, but it can also damage the intake valves.

Possible causes of burnt valves are:

To help prevent this type of failure, there are a few things you can do:

  • Maintain a clean, efficient cooling system so the engine does not run too hot.
  • Use good quality fuels to help prevent carbon build up on the valves, and regularly check the valve clearances.
  • Irregular valve sealing with cylinder head valve seat. Carbon residues generated by irregular combustion will jeopardize the sealing between the valve and its seat.
  • Incorrect valve clearance can jeopardize the valve sealing and also cause this type of failure.
  • Running a dry fuel such as L.P.G resulting in inadequate lubrication.

Deposits can travel to other areas of the engine and cause problems, too. Because engine deposits build up slowly, you can go a long time without noticing they’re there. Eventually they’ll rob your engine of its power and can cause serious hesitation and stalling if left unattended.

Carbon On Valves
Carbon On Valves

Minimizing Carbon Deposits

Although additives have been around for a few decades now, it wasn’t until recently that they actually worked quite well. I am not going to name or suggest any because they all say they work.

Just remember even though most do work they also have a down side as well. I would go by word of mouth as seeing is believing.


  • Using name-brand gasoline that contains a fuel system cleaner.
  • Limiting idling time and cold starts.
  • Employing high-quality oil and keeping the carburetor/fuel injection system tuned properly.

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