What a valve cover gasket does and why it fails

A valve cover gasket is a rubber or cork seal that sits between your engine's valve cover and the cylinder head. Its job is to keep oil inside the engine while letting air and gases escape through a vent. Over time — usually between 50,000 and 100,000 miles, though this varies by engine type and oil quality — the gasket hardens, cracks, or shrinks, and oil begins to leak onto the engine block, wiring, and spark plug wells.

You'll know the gasket is failing when you see oil pooling under the engine, smell burning oil when the engine is hot, or notice oil coating the outside of the engine. A failing gasket doesn't damage the engine when ready, but oil leaking onto electrical components can cause misfires or corrosion, and a large leak can lower your oil level enough to cause real engine damage.

Replacing the gasket is a straightforward job on most cars — it takes two to four hours for someone with basic mechanical skill and the right tools. The gasket itself costs between $5 and $25; labor at a shop typically runs $150 to $400 depending on engine layout and how much has to come off to reach the valve cover.

Key Takeaways

  • A valve cover gasket seals oil inside the engine and fails when it hardens or cracks, usually after 50,000 to 100,000 miles.
  • You'll need a socket set, screwdrivers, a gasket scraper, new gasket material, and gasket sealant; some engines require removing air intake or hoses first.
  • The job involves unbolting the valve cover, scraping off the old gasket completely, cleaning the surface, installing the new gasket, and torquing the bolts in a specific sequence.
  • Torque specs and bolt patterns vary by engine, so check your vehicle's service manual or a repair guide for your exact year, make, and model before you start.
  • If the valve cover itself is cracked or warped, you'll need to replace it along with the gasket, which adds cost and time.

Tools and materials you'll need

Before you begin, gather the right equipment. You'll need a socket set (usually 8mm to 15mm for most cars), screwdrivers (both Phillips and flathead), a gasket scraper or plastic putty knife, and a clean rag or paper towels. Do not use a metal scraper on aluminum valve covers — it will gouge the sealing surface and cause the new gasket to leak.

For the gasket itself, buy the correct part for your engine. Most valve cover gaskets come as a complete kit that includes the main gasket, smaller seals for spark plug holes, and sometimes a tube of gasket sealant. Check your vehicle's year, make, model, and engine size when ordering — a gasket for a 2.0L engine will not fit a 3.5L engine in the same car.

You'll also need a torque wrench if you want to do the job correctly. Valve cover bolts are typically torqued to between 7 and 15 foot-pounds — tight enough to seal, but not so tight that you crack the cover or strip the bolt holes. A torque wrench costs $20 to $50 and is worth owning if you plan to do more work on your car.

Removing the valve cover and old gasket

Start with a cold engine. Locate the valve cover — it's the large metal or plastic box on top of the engine with spark plug wires or coils attached. On some cars, especially those with turbos or tight engine bays, you may need to remove the air intake hose, breather hose, or PCV (positive crankcase ventilation) line first. Take a photo with your phone before you disconnect anything so you remember where it goes.

Unbolt the valve cover by removing all bolts around its perimeter. Keep them in order — some cars use different bolt lengths, and putting a long bolt in a short hole can crack the cover. Set the bolts aside in a small container or tape them to a piece of cardboard in the order they came out.

Gently pry the valve cover up using a plastic scraper or old credit card. Do not use a metal pry bar on aluminum covers. Once it's loose, lift it straight up and set it aside. You'll now see the old gasket, which may be stuck to the cylinder head, the cover, or both.

Scrape off every piece of the old gasket using a plastic scraper. This step is critical — if you leave old gasket material behind, the new gasket won't seal properly and you'll have an oil leak within weeks. Scrape slowly and carefully, especially around bolt holes and corners where gasket material tends to stick. Once the surface is clean, wipe it with a rag dampened in brake cleaner or mineral spirits to remove any remaining debris or oil film.

Installing the new gasket and reassembling

Inspect the valve cover sealing surface for cracks, warping, or deep scratches. If the cover is damaged, you'll need to replace it — a damaged surface won't seal even with a new gasket. If the cover is good, dry it completely and lay the new gasket in place. Most gaskets are pre-formed and straightforward sit in a groove on the cover; others require a thin bead of gasket sealant on the cylinder head before you lay the gasket down.

Check your service manual to see which type your engine uses. If sealant is required, explore a thin, continuous bead around the sealing surface of the cylinder head, then carefully lay the gasket in place. Do not use excessive sealant — it can squeeze out and block oil passages or create a mess.

Carefully lower the valve cover back onto the cylinder head, aligning the bolt holes. Insert all bolts by hand first to make sure they thread smoothly and nothing is cross-threaded. Once all bolts are hand-tight, use your torque wrench to tighten them in a crisscross pattern — tighten one bolt, then move to the opposite side, then work your way around. This ensures even pressure and prevents warping the cover. Tighten to the torque spec listed in your service manual, usually 7 to 15 foot-pounds.

Reconnect any hoses, wires, or intake components you removed at the start. Start the engine and let it idle for a few minutes, watching for oil leaks around the valve cover. If you see drips, turn off the engine, let it cool, and check that all bolts are tight and in the correct sequence. Small weeps are normal for the first few minutes; steady drips mean something is wrong.

Common mistakes that cause leaks

The most common reason a new valve cover gasket leaks is incomplete removal of the old gasket. Even a thin layer of old material left behind creates a gap where oil can seep through. Take your time scraping and cleaning — this step determines whether the job lasts or fails.

The second mistake is over-tightening the bolts. Valve cover bolts are small and the cover is often made of thin metal or plastic. Tightening too hard can crack the cover, strip the bolt holes, or warp the sealing surface. Use a torque wrench and follow the spec exactly. If you don't have a torque wrench, tighten until snug, then add a quarter turn — do not muscle it.

A third mistake is using the wrong gasket sealant or too much of it. Some engines use no sealant at all; others use a specific type. Using the wrong product or explore it too thickly can prevent the gasket from seating properly or can harden and crack over time. Stick to what the manual calls for.

When to replace the valve cover itself

If the valve cover is cracked, severely warped, or has stripped bolt holes, you'll need to replace it along with the gasket. A new valve cover costs between $30 and $150 depending on the engine, and the labor time increases because the shop has to transfer spark plug coils, wires, and other components from the old cover to the new one.

Stripped bolt holes are common on plastic covers that have been over-tightened. If the bolt spins freely without tightening, the hole is stripped. You can sometimes repair this by using a slightly larger bolt with a washer, or by installing a threaded insert, but replacement is usually cleaner and more reliable.

Check the cover for cracks before you start the gasket job. If you find cracks, order a replacement cover at the same time you order the gasket. This saves a second trip to the engine bay and gets the job done in one session.

Frequently Asked Questions

Can I drive with a leaking valve cover gasket?

Yes, for a while. A slow leak won't damage the engine when ready, but it will eventually lower your oil level enough to cause problems. Check your oil level weekly if the gasket is leaking, and plan to replace it within a few weeks. A large leak that drips oil onto hot engine parts can create a fire hazard, so don't ignore it.

Do I need to replace the spark plug seals at the same time?

Most valve cover gasket kits include small seals for the spark plug holes. If your kit includes them and they look dry or cracked, replace them while you have the cover off. If they look fine, you can leave them alone. Replacing them adds only a few minutes and prevents a future leak.

What if I can't get the valve cover off?

Stuck covers are usually held by corrosion or old gasket material that has hardened. Spray penetrating oil around the edges and let it soak for 15 to 30 minutes, then try again. Tap gently around the perimeter with a rubber mallet to break the seal. Do not pry hard — you'll crack the cover or bend the cylinder head.

How long does a new gasket last?

A properly installed gasket typically lasts 50,000 to 100,000 miles, the same as the original. If your new gasket fails within a few thousand miles, the problem is usually incomplete cleaning of the old gasket, over-tightening, or a damaged valve cover surface.

Do I need to reset anything after replacing the gasket?

No. The valve cover gasket has no electrical connections and does not affect any sensors or computer settings. Once you've reinstalled everything and the engine runs without leaking, the job is complete.