Sticking Valves From Carbon Deposits: Reasons & How To Fix

The combination of heat, oxygen, pressure and any kind of fuel (even the firewood in your fireplace) will create carbon deposits. A perfect place for carbon deposits to buildup very quickly is your car engine’s combustion chamber, where all the above elements are present. 

Excessive carbon deposits can create numerous problems for engine performance and fuel efficiency, some of which stem from valves sticking open. Fortunately, the formation of carbon deposits can be lessened by a few preventative measures, and you can fix sticky valves in your own garage with this comprehensive article on engine maintenance.

The Reasons and Consequences of Carbon Deposits

As mentioned, the internal combustion engine is a perfect place for the formation of carbon deposits, particularly on the intake valves, EGR valves, injector nozzles, and pistons. The valve slides up and down inside the valve guides of a cylinder head dozens of times per second in a hot, gaseous environment. Over time, carbon deposits and other impurities, like resin deposits left by oil, can work their way into the tiny space between the valve and valve guide, causing the valves to stick and thus not closing properly. 

Certain driving habits can cause carbon to build up faster, including excessive idling, going for short trips, driving mostly in stop-and-go traffic, and using low grade fuel which usually has more contaminants. 

Impact on Engine Performance 

Carbon deposits in the combustion chamber are almost inevitable due to the combination of all the right elements. To a certain extent, carbon deposits will start to hinder your engine’s performance and fuel economy. 

Carbon buildup in the combustion chamber can disrupt normal airflow. The resulting turbulence causes the air and fuel to mix unevenly, so the air and fuel mixture needed for combustion is rich in certain areas and while others might be lean. This sub-optimal combustible mixture will create hotspots in the combustion chamber and consequently, the mixture might ignite before the spark plug fires, which is an engine pre-ignition problem. This leads to engine inefficiencies and may cause permanent engine damage if the problem prolongs.

A sticky valve from carbon deposits might not close properly, leading to failing engine temperature sensors. This can result in rough idling at start-up when the engine is cold.

Symptoms of Sticky Valves from Carbon Deposits

A sticky valve from carbon buildup can make several internal components of the engine stop working properly and manifests as one or more of the following symptoms: 

• Rough cold idle: due to engine temperature sensors not working properly.

• Clicking noise: A sticky valve sticking will typically create a clicking noise that regularly occurs every two to three seconds at idle, particularly with a cold start. As the engine rpm increases, you will most likely hear more rapid clicking noises, but it may or may not get louder.

• Engine misfires: your engine may jump up and down, causing your car to start and stop suddenly.

• Hard engine starts

• Black exhaust clouds under hard acceleration

• Decreased acceleration or hesitation when accelerating

• Check engine light illuminates on dashboard

Prevention

Though carbon deposit is inevitable, you can limit its formation by avoiding excessive idling, avoiding making short trips by combining errands to drive longer distances each time, limiting cold starts, using better quality gasoline that contains a fuel system cleaner plus using better oil, and keeping the carburetor and fuel injection system tuned properly.

How To Fix A Sticky Valve From Carbon Deposits

Step 1 – Starting the engine and listening for clicking noises

Set your car in park and engage the emergency brake. Start the engine and allow it to warm up to normal operating temperature while raising the hood. 

Look for the valve cover, which is a long rectangular box on the top of the engine. Use a stethoscope to listen for any muffled clicking noises coming from it. Sometimes, a valve that is stuck or only moves up and down slightly might make a popping noise.

Step 2 – Restoring proper engine oil level

Shut the engine off. Open the crankcase to check the engine oil level.  A very low oil level will cause all of the lifters to click, causing a machine-gun like clicking that comes from both the front and rear of the engine. 

If needed, fill the oil up to the line on the dipstick scale that is marked with the word “hot”. Start the engine again, allow it to warm up and see if the noise persists after the  proper oil refill.

Another scenario is that the oil level is higher than the “hot” mark, which can allow air bubbles to enter the system. In this case, drain off the oil from the crankcase until it reaches the “hot” mark on the dipstick.

Step 3 – Adding oil additive

Add a full can of oil additive to the crankcase. Engine oil additives are chemical compounds that improve the lubricant performance of the existing base oil. They contain antioxidants, corrosion inhibitors, anti-foaming agents and demulsifying agents.

The oil additive will penetrate deep into the valve and lifter areas to lubricate and allow the sticky valves to move up and down properly again. After adding the oil additive, go for a few hours drive on the highway with some hard acceleration. Avoid lugging the engine (that is when you’re puttering along in a higher gear than you need to be in and the engine is turning low RPMs, which means the engine has to work harder to do the same job). When you’re done, wait for the engine to cool down before changing the oil and filter. If the sticky valve situation is not too serious, it should be resolved by now.

Step 4 – Lubricating the Valve Springs

When the engine has cooled down, use a socket to remove the valve cover. Look for the thick valve springs and spray penetrating oil inside the spring, where the shiny valve stem sits (it has a diameter the size of a pencil). Let the penetrating oil sit for several minutes for deep penetration. While you’re at it, check if all of the small retainer clips that sit on the top of each valve to hold it in place are in their proper position. 

Use a small hammer to gently tap on the top of the valve springs to help freeing up the valve stem shaft so that the sticky valve can move properly. Now that you’re done, replace the valve covers and start the engine to check if the clicking noise persists.