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

The valve seals ensure that the oil stays in the crankcase and does not enter the cylinders. Here's how to tell if your car has a bad valve seal

Symptoms Of A Bad Valve Seal

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

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

The highest concentration of wear in a vehicle is found in the engine. As the engine heats up and generates a lot of pressure, some components inevitably lose their integrity.

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

The valve seals are vital to holding the engine oil and the car engine’s pressure on separate sides. It is not very common with bad valve seals in modern engines, but it happens. Let’s take a quick look at 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, bad fuel consumption, or rough idling are other signs to look for when your valve seals are bad.

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

Bad Valve Seals Symptoms

1. Blue Smoke From Exhaust

Oil Leak On Floor

The most common symptom of a bad valve seal is blue smoke from the exhaust pipe. This can either be caused by a leak of the intake valve seal, which causes the engine to consume and burn oil inside the combustion chamber.

It can also be an exhaust valve seal leaking, which will push oil directly out to the exhaust pipe, causing it to evaporate.

As the problem worsens, the smoke becomes 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 On Spark Plugs

If you recently replaced your spark plugs and noticed that it was some strange clay on the spark plug tips – it is most likely coming from burnt oil after the combustion.

This oil will burn into the spark plug and cause clay, which will stay there. This oil is most likely coming from a leaking intake valve sealing or a failed turbocharger.

3. Bad Oil Consumption

Bad Oil Consumption E1609873549750

As we discussed before, both a leaking intake or exhaust valve will cause the engine oil to pour out into the exhaust pipe.

A normal engine contains around 4 liters of engine oil, and if you keep driving your car with leaking valve seals, you may notice the oil level going down.

If you notice bad oil consumption together with any of the other symptoms here, it is a good time to give your car to a mechanic for a look.

4. External Oil leaks

Oil Leak On Floor E1609873630617

If you have a turbocharged car, the turbo pressure can go past the intake valve seals if worn, which causes the pressure in the crankcase house to increase.

Increased crankcase pressure can result in external oil leaks from different engine sealings and even cause sealings to pop out completely from the engine.

5. Rough Idling

Car Engine Rough Idle E1609793094987

A defective valve seal is easily noticeable when your car is idling. The car engine is often susceptible to holding a steady low, idling RPM.

Because of this, when a valve seal is bad, and there is oil going into the combustion chamber, you might notice rough idling or even stall sometimes.

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

If you experience rough idling together with blue smoke, it is definitely time to check your valve seals.

6. Loss in Acceleration

Car Acceleration E1609869867245

The valve seals can also be so bad that the valves, spark plugs, and catalytic converter gets clogged with burnt oil.

This can cause a heavy performance issue with your car, and it can feel much slower than usual, 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 valve seal aims to separate the intake flow and the exhaust flow entering the crankcase. It is also vise versa – for not letting oil going into the cylinders and out through the exhaust.

The valve seals are made of a metallic outer ring and a high heat-resistant rubber sealing against the valve.

Valve seals rarely go bad on modern engines, but it can happen in some rare cases.

Valve seal location

Valve Seal Location E1609873724938

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

They are located under the valve springs, so you might have to remove the valve cover to see them. They are located under the valve springs, so you have to remove the valve springs to reach them.

Valve Seal Replacement Cost

The average valve seal replacement cost is between $250 and $2100 for all valve seals, depending on the car model and labor costs. The valve seals are cheap, and you can expect a cost of $50 to $100 for all of them. The labor cost is often between $200 and $2000.

To replace the valve seals, you have to 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 removing the cylinder head completely – but sometimes you have to remove the whole cylinder head.

This can, of course, be very time consuming, and it can take a lot of hours to replace the valve seals.

If you can do the job by yourself, you can do it cheaply because the cost of the valve seals is pretty cheap – it is the time to replace them that costs.

Worn valve seals are not a very common problem and since the high replacement cost – do proper research before you want to replace the valve seals.

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Written by:

Magnus is the owner and main author of MechanicBase. He has been working as a mechanic for over 10 years, and the majority of them specialized in advanced diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.