A valve cover gasket is one of the most common sources of engine oil leaks—and also one of the most misunderstood. Many owners replace the valve cover gasket again and again… only to see the oil leak return.
The real reason? Most of the time, the problem is not the gasket. It’s the valve cover itself.
This complete guide explains:
- What a valve cover gasket is and how it works
- Common valve cover gasket failure signs
- Why replacing the gasket doesn’t stop the leak
- How to diagnose a warped valve cover
- When upgrading to an aluminum valve cover is the correct fix
- Recommended billet/cast valve covers for Cummins, Powerstroke, Hemi, Duramax, SBC & BBC
1. What Is a Valve Cover Gasket?
A valve cover gasket seals the mating surface between the valve cover and the cylinder head. Its job is to:
- Prevent engine oil from leaking out
- Maintain crankcase sealing
- Keep contaminants from entering the valvetrain
The gasket must survive:
- High heat
- Constant vibration
- Oil exposure
- Crankcase pressure changes
2. What Is a Valve Cover?
A valve cover protects the valvetrain and provides the sealing surface the gasket presses against. On many modern engines, the cover also integrates:
- PCV/CCV passages (See why an Oil Catch Can is important)
- Oil baffles
- Ignition coil mounts (gas engines)
- Injector harness channels (diesel engines)
If the valve cover warps or cracks, even a brand-new gasket cannot seal properly.
3. Types of Valve Cover Gaskets
- Rubber – common, flexible
- Cork – used on SBC/BBC classic engines
- Silicone – heat-resistant
- Molded rubber with steel carrier – used on late-model engines
Heat cycles, crankcase pressure, and surface imperfections all accelerate gasket failure.
4. Symptoms of a Blown Valve Cover Gasket
- Oil on top of the engine
- Burning oil smell
- Oil in spark plug wells (Causing misfires)
- Oil dripping onto exhaust manifold
- Oil around turbocharger (diesel)
- High crankcase pressure or Check Engine Light
If the leak returns after replacing the gasket, the valve cover is very likely the issue.
5. Why Valve Cover Gaskets Fail (Real Cause)
Contrary to popular belief, the gasket itself usually is not the root cause.
The #1 cause of recurring leaks: A warped, cracked, or heat-deformed valve cover.
Common reasons valve covers deform:
- Constant heat cycles
- Plastic/composite covers swelling with age
- Diesel engine vibration
- PCV/CCV pressure buildup from carbon build-up
- Overtightened bolts
- Turbocharger radiant heat
If the valve cover isn’t perfectly flat, no gasket can seal properly.
6. How to Confirm If Your Valve Cover Is Warped
Tools Required:
- Straightedge
- Feeler gauge (0.002–0.008 inch)
Procedure:
- Remove valve cover
- Clean sealing surface
- Place straightedge across sealing edges
- Insert feeler gauge under gap
If you can fit a 0.003–0.006 inch gauge underneath, the valve cover is warped and cannot seal—even with a new gasket.
7. When Should You Replace the Valve Cover?
- Repeated gasket leaks (2nd or 3rd replacement)
- Warped or uneven sealing surface
- Cracks in the cover
- PCV/CCV failure inside the cover (Consider a CCV Reroute)
- You run high boost / towing applications (diesel engines)
Aluminum valve covers eliminate warping and permanently solve recurring leaks.
8. Benefits of Upgrading to an Aluminum Valve Cover
- Perfectly machined sealing surface
- No warping under heat
- Better sealing accuracy
- Higher PCV/CCV stability
- More durable for diesel vibration
- Cleaner engine bay appearance
Once you install an aluminum Valve Cover, your valve cover gasket can finally do its job.
9. Recommended SPELAB Valve Covers
Cummins Diesel
- Billet Aluminum Valve Cover for 2003–2005 Dodge Ram 5.9L Cummins
- Billet/Cast Aluminum Valve Cover for 2006–2024 5.9L/6.7L Cummins
- Oil Catch Can for 5.9L / 6.7L Cummins
Hemi Gen III (5.7L / 6.1L / 6.4L)
Ford Powerstroke
- Billet Aluminum Valve Cover – 2004.5–2007 6.0L Powerstroke
- Billet Aluminum Valve Cover – 2008–2010 6.4L Powerstroke
GM Duramax
Chevy Big Block & Small Block
10. FAQ
Q: Can I reuse a valve cover gasket?
A: No—most are single-use and lose compression once removed.
Q: Why does my valve cover gasket keep leaking?
A: The valve cover surface is likely warped, preventing the gasket from sealing.
Q: Is RTV required?
A: Only in OEM-specified areas (corners). Do not coat the entire gasket.
Q: Are billet valve covers worth it?
A: Yes—especially on Cummins, Powerstroke, Hemi, and Duramax engines.
Conclusion
A valve cover gasket leak is extremely common, but the gasket itself is rarely the real failure point. If your leak keeps returning, the true fix is upgrading to a precision-machined aluminum valve cover.
For Cummins, Powerstroke, Hemi, Duramax, SBC, and BBC engines, an upgraded valve cover provides the permanent solution to repeated gasket leaks.
