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How to Diagnose Bad Leaking Valve Cover Gasket

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How to Diagnose Bad Leaking Valve Cover Gasket

Created on: 2018-01-17

Check out this video to learn how to diagnose a leak in your valve cover gasket. This video is applicable to most vehicles.

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Hi. I'm Mike from 1AAuto. We've been selling auto parts for over 30 years!

How to tell if your car needs new valve cover gaskets. So on the top of your engine – this here, we have a four cylinder inline engine, but it will be similar for other engines if they are V6s or V8s. Underneath this plastic cover there is a secondary cover that is actually covering all of your valve train components, and where that meets the top of the engine's head there is a gasket that seals and holds in the oil.

When this gasket fails, you'll get a bunch of oily residue leaking out. Because oil is sticky, dirt and debris will stick to it. This is the number one easiest way to tell that you need a valve cover gasket. It's very obvious that this is leaking. However, some other things that would be a problem attributed to a leaking valve cover gasket would be oil loss.

So if you're checking the oil regularly and the engine oil keeps going low, it could be leaking from the valve cover gasket. Also if you've got a rough running or engine misfire, the valve cover gasket also seals around where the spark plugs go into the engine, so there could be oil leaking down into the spark plug openings and then leaking past the spark plugs that will give you a rough running and misfire.

The valve cover gaskets are typically near the exhaust manifold, so if there's oil leaking – this exhaust manifold is of course hot when the engine is running. The oil will burn off and you'll get a burning oil smell. Sometimes you'll even see smoke coming from underneath the hood and a faint whiff of burning oil. Worst case scenario: if this is really leaking very badly it could cause a fire.

Some engines have plastic covers over the valve cover gasket, so this is basically just like an appearance cover. What I'm going to do is remove it so we can get a closer look. Now you can better see the top of this engine. Some engines use a plastic valve cover. This one is aluminum. It matches the same metal that the engine is made out of. There is some oil that's been spilled from when the cap has been off, when the oil has been added to the engine, spilled underneath the oil fill cap, but the majority of this oil is coming from a failed gasket, because you can see the seam between the valve cover and the engine head, so the gasket seals between that seam. It goes all the way around. You can see some oil leaking in the back.

This is what a valve cover gasket can look like. It's kind of looped around here, so this is flexible rubber. It would be in the outline of the valve cover. Just the way it's packaged in here, it kind of looped around. Then in the center part there are little seals for each spark plug. Some valve cover gaskets, these are all one piece. Sometimes these come separately as little O-rings that need to be replaced, but they all work in the same manner. In this particular one it's all one piece, so it would be pretty easy to change. In an overhead cam engine like this, where it's a four cylinder and the valve cover is right on top, these valve cover gaskets are very easy to change. The V6 valve cover gaskets or V8 valve cover gaskets can be a little more difficult. You might have to remove the intake, but they're a pretty simple procedure for anyone that wants to do it at home.

Right here on your valve cover is the PCV valve, or positive crankcase vent. This vents pressure from the engine back into the intake manifold. This can get clogged over time and dirty. If it gets clogged up and the pressure can't vent it will push the crankcase pressure out of the valve cover gasket. That could also cause a valve cover gasket leak, so these should be changed according to your owner's manual.

Just in general what you do on your engine is if you've got coils in the top just like this you'd remove each coil pack. You can leave the spark plugs in the head. You don't need to take them out. The spark plugs are underneath the coils. You'd find all the valve cover bolts that are holding it on. You'd loosen all of those. You'd loosen all of the vacuum hoses, any type of electrical harnesses that are bolted to it. This is a PCV valve on this engine. You'd get those all out of the way.

You'd remove your valve cover. You don't need to drain the engine oil because when the engine is cold all the oil is in the pan. You can take your valve cover off, replace the seal. You'd need to remove the old one. It can be dried in there. You might have to work at it to get it out. Then you'd put your new seal in, replace the valve cover, tighten all your bolts. Reinstall your coil packs and any hoses you may have taken off. Then you can clean with brake parts cleaner around the engine and get rid of any excess oil that's been spilled here. You could use an engine degreaser, anything. You just want to clean up all this oil so that if the valve cover gasket fails at any point in the future you'll be able to tell because you'll see the fresh oil.

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