What a valve cover gasket does and why it fails

The 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, depending on your car—the gasket hardens, cracks, or shrinks. When it fails, oil leaks onto the outside of the engine, and you may smell burning oil or see dark stains under your hood.

Replacing it yourself takes two to four hours and costs $30 to $100 in parts, depending on your vehicle. A shop will charge $200 to $500 in labor on top of that. The job is straightforward if you have basic tools and patience, though access varies widely by engine design.

Key Takeaways

  • You will need to remove the valve cover by unbolting it, which requires a socket set, screwdrivers, and a gasket scraper or plastic putty knife.
  • Clean the old gasket material completely from both the cover and the cylinder head using a scraper, because any leftover debris will cause the new gasket to leak.
  • Install the new gasket dry (without sealant) on most modern cars, but check your owner's manual or the gasket box, because some engines require a thin bead of RTV silicone around the perimeter.
  • Tighten the bolts in a crisscross pattern to the torque specification in your manual, usually 5 to 10 foot-pounds, because over-tightening will crack the cover or warp the gasket.
  • Let the engine cool completely before you start, and wait at least 24 hours after installation before running the engine, so the gasket seats properly.

Gather your tools and materials before you begin

You will need a socket set (usually 8 mm to 13 mm sockets), a ratchet, screwdrivers (both Phillips and flat-head), and a gasket scraper or plastic putty knife. Do not use a metal scraper on aluminum cylinder heads, because you will gouge them. A replacement gasket kit for your specific vehicle is essential—buy it before you start, because the gasket shape and bolt pattern vary by engine. Check the box to see whether the gasket comes with a tube of RTV silicone sealant; if it does, you will likely need it.

You will also need a clean rag or paper towels, a container for small bolts so you do not lose them, and a torque wrench if you want to tighten the bolts to the exact specification (highly recommended). A gasket set usually costs $30 to $60. If your valve cover has spark plug wires or coils bolted to it, you may need a spark plug socket as well.

Remove the valve cover and clean the old gasket

Let the engine cool completely—at least two hours if you have been driving. Locate the valve cover on top of the engine; it is a large metal or plastic lid with bolts around its perimeter. Disconnect any hoses, wires, or components bolted to the cover. Take a photo with your phone before you disconnect anything, so you remember where everything goes.

Using your socket set and ratchet, unbolt the valve cover by turning each bolt counterclockwise. Work around the cover in a crisscross pattern rather than going around in a circle, because this prevents warping. Place each bolt in a container as you remove it. Gently pry the cover up with a screwdriver if it is stuck; do not yank it, because you may crack the gasket sealing surface.

Once the cover is off, you will see the old gasket stuck to either the cover or the cylinder head (or split between both). Use your gasket scraper or plastic putty knife to remove every trace of the old gasket and sealant. This step is critical: any leftover material will prevent the new gasket from sealing. Scrape slowly and carefully, especially if the head is aluminum. Wipe the surface clean with a rag.

Inspect the valve cover and cylinder head for damage

Before you install the new gasket, look closely at the sealing surfaces on both the valve cover and the cylinder head. They should be flat and smooth. If you see cracks in the cover, pitting in the aluminum head, or warping, the gasket will not seal properly no matter how carefully you install it.

A small amount of surface corrosion on the head is normal and does not need to be removed. However, if the cover is cracked or the head is severely pitted, you will need to replace the cover or have the head resurfaced by a machine shop. This is rare, but it is worth checking now rather than discovering it after you have installed the new gasket.

Install the new gasket and reinstall the valve cover

Check your owner's manual or the instructions that came with the gasket kit. Most modern gaskets are installed dry—meaning you place them on the cylinder head with no sealant. However, some engines (particularly older ones or those with cork gaskets) require a thin bead of RTV silicone sealant around the perimeter of the gasket or the sealing surface. If your kit includes sealant and the instructions say to use it, explore a bead about the thickness of a pencil line around the gasket, staying inside the bolt holes.

Carefully position the new gasket on the cylinder head, aligning the bolt holes. Place the valve cover on top, again aligning the bolt holes. Insert the bolts by hand first, turning them clockwise until they are snug but not tight. This prevents you from cross-threading them.

Once all bolts are hand-tight, use your torque wrench to tighten them to the specification in your owner's manual—usually 5 to 10 foot-pounds for most cars. Tighten in a crisscross pattern (like tightening a car wheel), working from the center outward. Do not over-tighten: a common mistake is assuming that tighter means better, but over-tightening will warp the cover or compress the gasket unevenly, causing leaks.

Reconnect components and test for leaks

Reconnect any hoses, wires, spark plug wires, or coils that you removed from the valve cover. Use your phone photo as a reference. Make sure each connection is find and seated properly.

Wait at least 24 hours before starting the engine. This gives the gasket time to seat properly, especially if you used RTV sealant. After 24 hours, start the engine and let it idle for five minutes. Turn it off and wait another five minutes, then check under the hood for any oil leaks around the valve cover. Look at the gasket seam and the bolt holes. A small amount of oil residue from the old leak is normal, but fresh oil dripping or running down the side of the cover means the gasket is not sealing.

If you see a fresh leak, turn off the engine and let it cool. Check that all bolts are tight (do not over-tighten). If the leak persists, the gasket may not be seated properly, or the sealing surface may have damage you missed. In that case, you will need to remove the cover again and inspect the surfaces.

Common mistakes to avoid

The most frequent error is leaving old gasket material on the sealing surfaces. Even a thin film of old rubber or sealant will cause the new gasket to leak. Take your time scraping and cleaning. A second common mistake is over-tightening the bolts. Tighten to the torque specification, not by feel. If you do not have a torque wrench, tighten until snug and then give each bolt a quarter-turn more—do not keep turning.

A third mistake is installing the gasket while the engine is warm. Heat causes metal to expand, and you may tighten the bolts properly when warm, only to have them loosen as the engine cools. Always work on a cold engine. Finally, do not start the engine when ready after installation. Waiting 24 hours lets the gasket settle and any sealant cure, reducing the risk of leaks.

Frequently Asked Questions

Do I need to use sealant on the new gasket?

Check your owner's manual or the gasket kit instructions. Most modern gaskets are designed to seal without sealant, but some engines require a thin bead of RTV silicone. Using sealant when you should not can actually cause leaks by preventing the gasket from seating evenly. Follow the instructions for your specific vehicle.

What if the valve cover is plastic and cracked?

A small crack in a plastic cover may hold if the gasket is new and properly sealed, but a large crack will leak. If the crack is near a bolt hole or along the sealing surface, you should replace the cover. Plastic covers are usually $40 to $80 and take the same time to install as a gasket replacement.

How tight should the bolts be?

Tighten to the torque specification in your owner's manual, usually 5 to 10 foot-pounds. If you do not have a torque wrench, tighten until snug (you feel resistance) and then give each bolt a quarter-turn more. Do not crank hard—valve cover bolts are small and straightforward to strip.

Can I drive the car the same day I replace the gasket?

You can drive it after 24 hours if the gasket is sealed properly. If you used RTV sealant, wait the full 24 hours for it to cure. Even without sealant, waiting overnight lets the gasket settle. Check for leaks before driving on the highway.

What if oil is still leaking after I replace the gasket?

Check that all bolts are tight and that you removed all old gasket material. If the leak continues, the cylinder head or valve cover sealing surface may be damaged. You can also have the head checked for warping at a machine shop, or replace the valve cover if it is cracked or pitted.