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6 Symptoms of a Bad Valve Seal (and Replacement Cost)

A vehicle has about 30,000 functional parts, large and small.

With so many parts, it’s no surprise that some parts wear out over time and need to be replaced.

The greatest concentration of wear on a vehicle is on the engine. As the engine heats up and builds up a lot of pressure, some components inevitably lose their integrity.

Valve seals are one of those components that can be affected by the heat and pressure of an engine after a long time.

Valve seals are essential for keeping engine oil and car engine pressure on separate sides. It’s not very common to have bad valve seals on modern engines, but it does happen. Let’s quickly review the signs to look for:

The most common symptom of bad valve seals is blue smoke from the exhaust pipe. You may also notice oil on the spark plugs if you inspect them. External oil leaks, poor fuel economy, or rough idling are other signs to look for when valve seals are damaged.

Here is a more detailed list of the 6 most common symptoms of a bad valve seal:

Symptoms of bad valve seals

1. Blue exhaust smoke

Oil leak on the floor

The most common symptom of a bad valve seal is blue smoke from the exhaust pipe. This can be caused by a leaking intake valve seal causing the engine to consume and burn oil within the combustion chamber.

It could also be a leaking exhaust valve seal, which will push the oil directly into the exhaust pipe and cause it to evaporate.

As the problem worsens, the smoke gets worse and worse. You will notice that the blue smoke lasts longer than before and does not disappear even at high speeds.

2. Oil-clogged spark plugs

Oil in spark plugs

If you recently replaced your spark plugs and noticed that there was foreign clay on the tips of the spark plugs, it is most likely due to burning oil after burning.

This oil will burn in the candle and produce clay, which will remain there. This oil is most likely coming from a leaking intake valve seal or a faulty turbocharger.

3. Poor oil consumption

Bad oil consumption E1609873549750

As we discussed above, a leaking intake or exhaust valve will cause engine oil to spill into the exhaust pipe.

A normal engine contains around 4 liters of motor oil, and if you continue to drive your car with leaking valve seals, you may notice the oil level dropping.

If you notice poor oil consumption along with any of the other symptoms here, now is a good time to take your car to a mechanic.

4. External oil leaks

Oil leak on land E1609873630617

If you have a turbocharged car, the pressure from the turbo can overcome the intake valve seals if they are worn, causing pressure to build up in the crankcase.

Increased pressure in the crankcase can cause external oil leaks from various engine seals and even cause engine seals to come off completely.

5. Hard slow motion

Rough Idle Car Engine E1609793094987

A bad valve seal is easily noticed when your car is idling. Often, the car engine is likely to maintain a low and constant idle speed.

For this reason, when a valve seal is bad and oil enters the combustion chamber, you can sometimes notice a rough idle or even stalling.

It can also be caused by clogged oil in the spark plugs, caused by faulty intake valve seals.

If you experience a rough idle with blue smoke, it’s definitely time to check your valve seals.

6. Loss of acceleration

Car acceleration E1609869867245

Valve seals can also be so bad that the valves, spark plugs, and catalytic converter become clogged with burned oil.

This can cause major performance problems in your car and it may feel much slower than normal, especially if your catalytic converter is clogged.

The function of a valve seal.

Valve seal around valve shaft
A valve seal around the valve shaft

The purpose of the valve seal is to separate the intake flow and exhaust flow entering the crankcase. It is also the other way around, to not let the oil enter the cylinders and come out through the exhaust.

Valve seals consist of a metal outer ring and a heat-resistant rubber seal against the valve.

Valve seals rarely fail in modern engines, but it can happen in rare cases.

Valve seal location

Valve seal location E1609873724938

Valve seals are located in the cylinder head, below the valve springs, installed around and sealing the valves.

They are located under the valve springs, so you may need to remove the valve cover to see them. They are located under the valve springs, so you must remove the valve springs to reach them.

Valve seal replacement cost

The average valve seal replacement cost is between $250 and $2,100 for all valve seals, depending on car model and labor costs. Valve seals are inexpensive and you can expect a cost of $50 to $100 for each. Labor costs typically range from $200 to $2,000.

To replace the valve seals, you must remove the valve cover to remove the valve springs so you can reach the valve seals.

In many cases, you can pressurize the cylinder chamber to remove the valve springs without completely removing the cylinder head, but sometimes it is necessary to remove the entire cylinder head.

Of course, this can be time-consuming and it can take many hours to replace the valve seals.

If you can do the work yourself, you can do it inexpensively because the cost of valve seals is quite low; what costs is the time to replace them.

Worn valve seals are not a very common problem and given the high replacement cost, do proper research before attempting to replace valve seals.


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