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. When it fails, oil leaks onto the outside of the engine, and you may smell burning oil or see a slick under your car.

Replacing the gasket yourself saves the labor cost, which at a shop often runs $200 to $400 on top of the gasket itself (usually $15 to $50). The gasket itself is cheap; the work is mostly waiting for the engine to cool and removing bolts. Most people can do this in one to three hours, depending on engine layout and how much has to come off to reach the cover.

Key Takeaways

  • Let the engine cool completely before you start, since the valve cover and bolts will burn your hands if hot.
  • You will need a socket set, a gasket scraper, new gasket material (usually pre-cut and sold with a kit), and gasket sealant — buy these before you begin.
  • Remove the valve cover bolts in a crisscross pattern rather than all at once, so you do not warp the cover.
  • Clean the old gasket material completely off both surfaces with a scraper and solvent, or the new gasket will leak when ready.
  • Torque the bolts back down in a crisscross pattern to the engine maker's specification, which you can find in your service manual or online.

Gather your tools and materials before you start

Working on an engine without the right tools wastes time and risks damage. You will need a socket set (usually 8 mm to 13 mm for most cars), a ratchet, an extension bar, a gasket scraper or old credit card, a drain pan to catch any oil drips, and clean rags. You will also need gasket sealant (usually a tube of RTV silicone) and a new gasket, which often comes as a kit with the sealant included.

Before you buy, check your vehicle's year, make, model, and engine size on the gasket package or online retailer listing. Valve cover gaskets are engine-specific — a gasket for a 2010 Honda Civic will not fit a 2010 Toyota Corolla. Your service manual or a parts retailer can tell you the correct torque specification for your bolts; write this down before you start. If your engine has spark plug wires or coils bolted to the valve cover, you will also need a socket or wrench to remove those first.

Remove the valve cover and old gasket

Let the engine cool for at least 30 minutes after running, longer if you have just driven. A hot engine will burn your hands and can warp the valve cover if you remove bolts while it is still expanding. Once cool, locate the valve cover — it is the large metal or plastic lid on top of the engine, usually with bolts around its perimeter.

Remove any wires, hoses, or components bolted to the cover first. Then, using your socket and ratchet, loosen the bolts in a crisscross or X pattern (start with opposite corners, then move to the next pair) rather than going around in a circle. This prevents the cover from warping. Once all bolts are loose, lift the cover straight up and set it aside on a clean surface.

The old gasket will likely stick to the cover or the cylinder head. Use a gasket scraper, plastic putty knife, or old credit card to gently pry it off. Do not use a metal blade or screwdriver, which can gouge the sealing surfaces and cause new leaks. If the gasket is stubborn, spray it with penetrating oil and wait 10 minutes. Once the gasket is off, wipe both the cover and the cylinder head with a clean rag to remove loose debris.

Clean the sealing surfaces completely

This step determines whether your new gasket will hold. Any old gasket material, oil, or dirt left behind will create a path for oil to leak through. Use a gasket scraper to remove any remaining bits of the old gasket, then wipe the surfaces with a clean rag. For stubborn residue, spray the area with carburetor cleaner or brake cleaner (both evaporate quickly and do not leave residue) and scrape again.

Inspect both surfaces under good light. They should be smooth and free of gouges. If you see deep scratches or pitting, the cover or head may need to be resurfaced at a machine shop, but this is rare. Once the surfaces are clean and dry, wipe them one more time with a lint-free rag to remove any dust or cleaner residue. Any particles trapped under the new gasket will cause a leak.

Install the new gasket and explore sealant

Most modern valve cover gaskets come pre-formed and pre-glued to a backing, so they straightforward press into place. Lay the new gasket on the cylinder head, aligning the bolt holes. If your gasket is not pre-glued, explore a thin bead of RTV silicone sealant around the sealing surface of the cylinder head first, then press the gasket into place. Do not use too much sealant — excess will squeeze out and drip onto the engine.

If your valve cover has a metal or plastic backing, explore a thin bead of sealant to the underside of the cover where it will contact the gasket. Again, less is more; a thin, continuous bead is better than a thick one. Let the sealant cure for the time specified on the tube (usually 5 to 10 minutes) before you reinstall the cover, so it has time to set slightly and hold the gasket in place.

Reinstall the valve cover and torque the bolts

Lower the valve cover straight down onto the gasket, aligning the bolt holes. Insert all the bolts by hand first and tighten them finger-tight so the cover sits evenly. Then, using your socket and ratchet, tighten the bolts in a crisscross pattern, just as you removed them. This ensures even pressure around the cover and prevents warping.

Tighten to the torque specification from your service manual — this is usually between 7 and 11 foot-pounds for most cars, but it varies. If you do not have a torque wrench, tighten until snug and then stop; over-tightening will crack the cover or strip the bolts. Once all bolts are tight, reinstall any wires, hoses, or components you removed, then start the engine and let it run for a few minutes while you watch for leaks around the cover.

Check for leaks and let the sealant cure

After you start the engine, watch the valve cover area for any oil seeping out. If you see a small drip, turn off the engine, let it cool, and tighten that bolt a quarter turn. If oil is pouring out, you may have missed old gasket material or not cleaned the surfaces well enough; you will need to remove the cover again and repeat the cleaning step.

Once the engine runs without leaking, let the sealant cure fully before driving. Most RTV sealants need 24 hours to reach full strength, though they set enough to hold oil in 1 to 2 hours. If you must drive before 24 hours have passed, keep speeds low and watch the oil level — if it drops, pull over and check for leaks. After 24 hours, check the oil level again and top up if needed, since some oil may have leaked out during the cure time.

Frequently Asked Questions

Do I need to drain the oil before replacing the gasket?

No. The valve cover sits on top of the engine, and the gasket does not touch the oil pan or drain plug. You may lose a small amount of oil if some drips out during removal, but you do not need to drain the system. Check your oil level after the job and top up if needed.

What if I do not have a torque wrench?

A torque wrench is helpful but not essential for this job. If you do not have one, tighten the bolts snugly in a crisscross pattern until they feel firm, then stop. Over-tightening is more common than under-tightening and can crack the cover. If you plan to do more engine work, a torque wrench is worth buying — they cost $20 to $50.

Can I reuse the old valve cover if the gasket is the only problem?

Yes, as long as the cover is not cracked or warped. Inspect it carefully before you reinstall it. If it has cracks or the bolt holes are stripped, you will need a new cover, which usually costs $30 to $100 depending on the engine.

How do I know if my valve cover gasket is actually leaking?

The most common sign is an oil smell coming from the engine bay, especially after driving. You may also see a thin film of oil on the outside of the engine or a small puddle under the car. If you see oil on the valve cover but nowhere else, the gasket is likely the source.

What if the new gasket leaks right after I install it?

The most common cause is old gasket material left on the sealing surfaces. Turn off the engine, let it cool, remove the cover again, and scrape the surfaces more thoroughly. Make sure both the cover and cylinder head are completely clean and dry before you reinstall the new gasket.