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Valve stem seals prevent oil from the cylinder head from seeping into the engine’s combustion chamber. These tiny, inexpensive seals are a critical part of your engine’s valvetrain.



What are Valve Stem Seals?

The top part of the valves, the stem side, rests inside the oily part of the cylinder head. The other side of the valve seals the combustion chamber when the engine is running. Valve stem seals keep the crankcase and combustion chamber separate and sealed off from one another.

How does a Valve Cover Gasket Work?

Valve stem seals prevent oil from contaminating the air/fuel mixture in the engine’s combustion chamber. They also prevent intake and exhaust gases from contaminating the oil in the cylinder head and the rest of the engine.

Valve stem seams are like any other round seal, only much smaller. The inside diameter fits over the valve stem. The outside diameter of the seal fits over the valve guide. Together, they form a tight seal between the crankcase and combustion chamber as the engine’s valves open and close.

How are Valve Stem Seals Made?

Like other circular seals found on a vehicle, valve stem seals often feature small springs that allow them to fit tightly over the parts they are designed to seal. Valve stem seals are mass-produced out of rubber, soft plastic, or nitrile on factory molding machinery.

Though you may not need to remove the cylinder head to complete a valve stem seal replacement, the job often requires special tools like a valve stem seal tool and a valve spring compressor.

Why do Valve Stem Seals Fail?

  • Valve stem seals often last more than 150,000 miles under normal driving conditions.
  • Infrequent oil and filter changes may cause valve stem seals to fail prematurely.
  • Improper installation often causes valve stem seals to fail shortly after installation.

What are the Symptoms of Valve Stem Seal Failure?

  • Blue or white smoke on start up that disappears when the engine reaches its normal operating temperature.
  • Excessive crankcase pressure caused by spent exhaust gas forcing its way past worn seals.
  • Engine may be difficult to start or run poorly due to insufficient compression in one or more cylinders.
  • Care must be taken to avoid mistaking leaking valve stem seals as leaky valves.

What are the Implications of Valve Stem Seal Failure?

  • Vehicle may fail state emissions tests.
  • Oil burning in the combustion chamber creates carbon deposits on the valves and piston crown.
  • The valves may fail to seal, resulting in a lack of compression and a poor running engine.
  • Excessive oil in the combustion chamber contaminates the spark plug, causing the cylinder to lose power.
  • Excess exhaust gases in the crankcase wreak havoc on other systems, making problems more difficult to diagnose.

If your vehicle smokes on start up, there’s a good chance one or more of your valve stem seals need to be replaced.

If you have questions or concerns about valve stem seals or any of your vehicle’s components, come into your local Pep Boys where we can answer any question, help you find any part, or perform any vehicle service you might need.