What a valve gasket does and why it fails

A valve gasket is a thin seal that sits between two metal parts of your engine — usually between the valve cover and the cylinder head — to stop oil from leaking out. Oil needs to stay inside the engine to lubricate moving parts. When a gasket wears out, cracks, or hardens, oil seeps past it and drips onto the engine block, the ground, or other components.

Gaskets fail because of age and heat. Every time your engine runs, it heats up and cools down, which causes the rubber or cork material in the gasket to expand and contract. After thousands of cycles, the material becomes brittle and loses its seal. A gasket can also fail if you over-tighten the bolts holding it in place, which pinches and damages the material.

You will notice a failing gasket by the smell of burning oil, visible oil pooling under your car, or oil on the outside of the engine. Some people ignore small leaks, but even a slow leak means you are losing oil over time, which can damage your engine if the level drops too far.

Key Takeaways

  • A valve gasket seals the gap between engine parts to prevent oil leaks, and it fails from heat cycles and age.
  • Replacing a valve gasket requires removing the valve cover, cleaning the old gasket material, and installing a new one with bolts tightened in a specific pattern.
  • The job takes two to four hours for most vehicles and costs between $150 and $400 in parts and labor at a shop, or $30 to $75 in parts if you do it yourself.
  • You will need basic hand tools, a gasket scraper, a new gasket, and possibly a new valve cover if the old one is warped or cracked.
  • Tightening bolts too hard is the most common mistake and will damage the new gasket when ready, so follow your vehicle's manual for the correct torque specification.

Tools and parts you need before you start

Gather your tools and parts before you begin. You will need a socket set and wrenches to remove the bolts holding the valve cover, a gasket scraper or plastic putty knife to remove the old gasket material, and a clean rag or paper towels. Do not use a metal scraper on the cylinder head surface, because you can gouge the metal and create a worse leak.

Buy a new gasket made for your specific vehicle year, make, and model — gaskets are not universal. The gasket kit usually comes with a new rubber seal and sometimes includes new bolts or washers. Check your vehicle's service manual to see if you also need a new valve cover; if the old cover is warped, cracked, or has a stripped bolt hole, replacing it at the same time prevents another leak soon after.

You may also want a torque wrench, which tightens bolts to a precise specification. This tool costs $20 to $40 and prevents the most common mistake: over-tightening, which crushes the new gasket and causes an when ready leak.

Steps to remove the old gasket and valve cover

Start by letting the engine cool completely — do not work on a hot engine. Disconnect the negative battery terminal to prevent accidental electrical shorts. Remove any hoses, wires, or brackets attached to the valve cover by unbolting or unclipping them. Take a photo with your phone before you disconnect anything, so you remember where each piece goes.

Unbolt the valve cover by removing the bolts around its perimeter. Keep the bolts in order — some engines have different bolt lengths, and putting a long bolt in a short hole can damage the threads. Lift the valve cover straight up and set it aside. If it sticks, tap it gently with a rubber mallet rather than prying, which can bend the cover.

Scrape away the old gasket material from the cylinder head surface using a gasket scraper or plastic putty knife. Work slowly and scrape in one direction to avoid gouging the metal. Wipe the surface clean with a rag and solvent or brake cleaner. The surface must be completely clean and dry before you install the new gasket, or the seal will not hold.

Installing the new gasket and reassembling

Place the new gasket onto the cylinder head, aligning it with the bolt holes. Some gaskets have a sticky backing that holds them in place; others require a thin bead of gasket maker applied to the cylinder head first. Check your gasket kit instructions to see which type you have.

Set the valve cover back on top of the gasket and insert the bolts. Tighten them in a crisscross pattern — start with the center bolts, then alternate to bolts on opposite sides, working toward the edges. This distributes pressure evenly and prevents the cover from warping. Tighten each bolt a little at a time in multiple passes rather than tightening one bolt all the way, then moving to the next.

Use a torque wrench to tighten the bolts to the specification in your vehicle's service manual. Most valve cover bolts are tightened to between 7 and 15 foot-pounds, but your manual will have the exact number. If you do not have a torque wrench, tighten the bolts until they are snug but not hard — you should be able to turn them with moderate hand pressure on the wrench, but not with your fingers alone.

Reconnecting hoses, wires, and brackets

Reattach any hoses, wires, or brackets you removed earlier. Use your phone photo as a reference to make sure everything goes back in the correct location. Reconnect the negative battery terminal. Start the engine and let it run for a few minutes while you watch for leaks around the valve cover. If you see oil dripping, turn off the engine and let it cool, then check that the bolts are tight.

Check the oil level with the dipstick after the engine has cooled for five minutes. Top it off if needed. Drive the car normally for a few days and check for leaks again. A small amount of oil residue around the cover is normal if the old leak was there for a while, but new oil should not be dripping.

When to take your car to a shop instead

Some vehicles have the valve cover in a location that is difficult to reach, or have many hoses and brackets in the way. If you do not have a service manual for your specific vehicle, a shop can look up the exact bolt torque specification and follow the correct reassembly order, which reduces the risk of a repeat leak.

If the valve cover itself is cracked, warped, or has stripped bolt holes, a shop can replace it at the same time. A new valve cover costs $40 to $150 depending on the vehicle, plus labor. If you attempt the job yourself and damage the cover while removing it, you will end up paying for a replacement anyway.

Labor at a shop typically ranges from $150 to $300, depending on how difficult the job is for your vehicle. Parts cost $30 to $75. The total bill is usually $200 to $400. If you do the work yourself, you save the labor cost but spend your time and take the risk of making a mistake that causes another leak.

Common mistakes that cause repeat leaks

Over-tightening the bolts is the most common cause of a leak that happens when ready after replacement. When you crush the gasket by tightening too hard, it cannot seal properly. Use a torque wrench or tighten by feel — snug but not hard — to avoid this.

Not cleaning the old gasket material completely is the second most common mistake. If bits of the old gasket remain on the cylinder head, the new gasket will not sit flat and will leak. Spend extra time scraping and wiping the surface until it is completely clean.

Installing the gasket upside down or misaligning it with the bolt holes will also cause a leak. Check your gasket kit instructions to see if the gasket has a correct orientation. Line up the bolt holes carefully before you install the valve cover.

Frequently Asked Questions

How long does a valve gasket last?

Most valve gaskets last between 80,000 and 150,000 miles, depending on your driving habits and how well the engine is maintained. Engines that run hot or are not serviced regularly may need a gasket replacement sooner. Once you replace one, the new gasket should last as long as the original if you do not over-tighten the bolts.

Can I drive with a leaking valve gasket?

You can drive short distances with a small leak, but the engine will lose oil over time. Check the oil level every week and top it off as needed. If the leak is large enough that you are adding oil every few days, stop driving and have it repaired, because running the engine low on oil can cause serious damage.

Do I need to replace the valve cover bolts too?

Most gasket kits include new bolts or washers. If your kit does not, you can reuse the old bolts as long as they are not stripped or bent. If a bolt is hard to turn or spins without tightening, replace it with a new one the same size and length.

What is the difference between a valve cover gasket and a valve gasket?

A valve cover gasket seals the valve cover to the cylinder head and is what this article describes. A valve gasket is a different part inside the engine that seals individual valves. Valve gaskets are much more difficult to replace and require removing the cylinder head, so the job is usually done by a shop.

Why is my new gasket leaking after I just replaced it?

The bolts are probably over-tightened, which crushes the gasket. Let the engine cool, remove the valve cover, and loosen the bolts slightly. Retighten them in a crisscross pattern to the correct torque specification. If the bolts are tight but the leak continues, the old gasket material may not have been completely cleaned from the cylinder head.