6 Signs of a Bad or Burnt Car Valves

Valves are part of the engine that helps with the combustion process. There are two types of valves. The valves that allow the air and/or fuel to enter the combustion chamber are called intake valves. The valves that are allowing the exhaust to leave the combustion chamber are called exhaust valves.

Both valves play a very important role and if one of them malfunctions, the engine will not work as it should. Luckily, there are signs of bad or burnt car valves that you can look out for.

Bad or burnt car valves can cause low engine power, misfire, air leaking through the exhaust or throttle body, rough idle, popping noise, and bad gas mileage.

6 Signs of a Bad or Burnt Car Valves

6 Signs of a Bad or Burnt Car Valves

Here are the 6 most common signs of a bad or burnt car valves:

1. Low power and misfire

When the intake or exhaust valves are bad, the engine will produce low power. Usually, this is caused by burnt valves. Basically, when combustion gases escape between the valve and valve seats, this will cause the exhaust gas to erode the exhaust valves causing premature failure.

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When valves are not sealing all the way, the cylinder compression will start to decrease therefore causing low power. You can run a compression test to determine which cylinder is causing the performance issue. The compression test can also diagnose and determine if there are any worn piston rings, worn cylinder walls, and bad head gaskets.

Conduct the compression test on all cylinders and compare the readings. If the compression is low, make sure there is no blue smoke coming out from the exhaust which is an indication of worn piston rings and cylinder wall. If the blue smoke from the exhaust lasts only 10 minutes, that means that the valve seals are bad. When white smoke appears from the exhaust after a compression test, that is a sign of a blown head gasket.

However, if there is a light white smoke coming out from the exhaust and smells like gasoline after the compression test, that is a sign that the valves are not sealing all the way and not all of the fuel is not burning in the combustion process. The unburned fuel will eventually cause the catalytic converter to fail. You should replace the valves to avoid premature parts wear.

Is your engine oil due for a change? Visit our Car Fluid Guide Website to learn the importance of changing your oil on time, which type of engine oil is best for your vehicle, and much more.

2. Air leaking at exhaust or throttle body

You can determine if a valve is bad or burnt by running an air leakage test.

  1. Rotate the crank pulley until the cylinder is on compression or power stroke.
  2. Make sure the intake exhaust valves are both closed.
  3. Remove the ignition coil and spark plugs.
  4. Use an air compressor and put air into the cylinder where the spark plugs are at.

If the exhaust valves are bad you will be able to hear air escaping through the exhaust pipe.

If the intake valves are bad you will be able to hear air escaping through the intake manifold and throttle body.

At this point, you should replace the bad valves and contain the air leakage.

3. Remove the cylinder head

Remove the cylinder head and inspect the valves for cracks and missing pieces. Take your time and perform a thorough inspection. Next, make sure all the valves are in a closed position so you can conduct a leakage test.

  1. To perform a leakage test you can use carburetor cleaner, brake cleaner, or lacquer thinner.
  2. Spray a good amount of the carb cleaner or pour the lacquer thinner on the valve seats.
  3. Let is sit for a few minutes.

If the valves are bad or burnt, the cleaning fluid will seep right through the valves and valve seats. At this point, the top end will need machine work.

4. Broken timing chain

A broken timing belt or timing chain system can cause the valves to impact against the cylinder head and bend or break all the valves for the interference engine. At this point, all of the damaged valves need to be replaced. The piston could also be damaged and if so, replacement is needed.

5. Rough idle, popping noise, and poor gas mileage

When the valves are bad, the engine performance will suffer. Bad or burnt valves will cause an increased fuel consumption and rough idle. Moreover, a popping noise can be heard.

At this point, it’s best if you conduct a compression test and an air leakage test to verify bad valves.

6. Valve noise

When valves make noise such as ticking, clacking, and chattering it can be due to low oil level or the valves are bad and need replacement.

First, check the oil level. If the oil level is good, then check for possible oil leaks. Next, if the engine has high mileage a valve adjustment might be needed.

How Car Valves Actually Work

The gases flow through the cylinder head, entering through the intake ports, and are exiting through the exhaust ports. The intake manifold and the air intake are located on one side of the engine, and the exhaust manifold on the other side. The job of controlling that flow of gases falls to the valves.

So, inside the ports, we just have a clear passage straight into the cylinder into the combustion chamber. The valves act to close that passage and open it at the appropriate time. The minimum number of valves that an engine needs are two, one intake valve and one exhaust valve.

The reason engines these days are almost all multi-valve engines with either four valves and sometimes five valves per cylinder is that you get a more efficient flow of gases in and out of the cylinder, which is what produces the power in the engine.

All the engineering in the valve goes into ensuring that we have an efficient flow of gases into the cylinder and out of the cylinder.

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Hi there. I am a certified Automotive Service Excellence (ASE) mechanic since 2018 and a car detailer for 10 years.

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