The Humble Mechanic: Replace a Leaking Valve Cover Gasket

The Humble Mechanic: Replace a Leaking Valve Cover Gasket

Charles shows our technician readers how to replace a valve cover gasket to fix an oil leak.

Today in the garage, I’m going to show you how to replace a valve cover gasket to fix an oil leak. Valve cover gaskets are probably one of the most common places for engine oil to leak.

The Miata is probably the easiest valve cover gasket in the entire world. Even if your car is a little different or a little harder, the steps and the processes that we use for this one can likely still be applied. For this one, we’re not going to need a ton of tools, but we want to make sure that we have brake parts cleaner and some rags to clean up any residual oil you might have on the engine.

As always, make sure you’re following the repair manual for your car. A quick tip on jobs like this — I love sliding a piece of cardboard under to catch any dirt or debris that might come off our engine when we’re cleaning it, and it’s a good idea to blow any dirt or debris off the valve cover before you start so that when you take it off, all the stuff that was on top of it doesn’t fall inside your engine.

Before we get our valve cover off, we need to remove all of the accessories that are attached to it. We’re going to start with our spark plug wires. Luckily ours are numbered and the lengths make it pretty easy to go back in the right spot.

If you need to though, go ahead and label your spark plug wires to make sure you get them back where they belong. Now, if you don’t have spark plug wires like this Miata, and you have coil on plug or some other version, you’re going to have to take those off and get them out of the way. What’s attached to the valve cover, of course, is going to vary by car and engine.

We also have our PCV valve that I’m going to take off as well as a hose on the other side, and one electrical connector. The Miata has two brackets at the back of the valve cover that we’re going to have to unbolt so we can get the valve cover out. They’re kind of hidden, but not too terribly tough to get to.

Now we can go ahead and unbolt our valve cover. You’ll want to go slow here. If any of the bolts are different lengths, keep them organized. In our case, it looks like all the bolts are the same length. Typically, you want to work from the outside bolts moving in. Sort of the opposite way we would when we torque the valve cover down. This is not always super vital, but it’s also a good habit to be in.

Now, before you go trying to pry and yank your valve cover off, do a double check and make sure you’ve got all your bolts, and none are hidden. Then I usually take a tiny pry bar and find a good, easy place to pry (Figure 1) where you’re not going to damage anything and gently pry up in a few spots, if you can, then once you’re loose, you can gently and carefully take off your valve cover.

Figure 1

Next, we’ll get our valve cover mating surface clean, starting by picking out any old leftover RTV. Make sure you don’t drop that stuff into your engine, and make sure you get the surface nice and clean for your new valve cover gasket.

Now, on to the valve cover. We’ll take our old gasket off all the way around. Sometimes there are captive bolts in some valve covers where the bolts go through. So be careful when you take the gasket out, you might lose all your bolts onto your bench.

Also, a tip, if your valve cover gasket is not all one piece like this one (Figure 2), make sure that you get new spark plug well gaskets. In addition to the corners, this is a common place for valve covers to leak. So, you wouldn’t want to just replace the outside and not these well gaskets.

Figure 2

Next, we’ll clean the inside of the valve cover as best we can. This is also the point where you want to really look for any damage to the valve cover, such as a crack. We would definitely not want to put a cracked valve cover back on our car. Now, before we put our new gasket in, I’m going to flip the valve cover over and do some basic cleaning to try and make it look a little nicer.

We’ll also hit it with a little bit of brake parts cleaner and then give it a little scrubby scrub (Figure 3). You can also use degreaser for this, if you’d like, just make sure you’re working in a well-ventilated area.

Figure 3

Once it’s clean, it’s time for our new gasket. I like to lay the gasket out and sort of test fit it to make sure I have it in the right orientation.

This one’s pretty easy because there are two humps on the front side and one hump on the backside. So you can’t put it on even remotely wrong. Before we get our gaskets set in the channels though, we need to do one final thing and let’s take a little bit of RTV in the corners of the gasket. We’re just going to work the gasket into the channels, making sure it’s pushing in as far as it’ll go. That’ll help when you install the valve cover that you don’t roll the gasket.

Now we are going to take our RTV and put it back in the corners on the cylinder head. Again, you don’t need a ton. Now get your valve cover. Make sure everything’s clean. Do another check and make sure that you are all tucked in with your gasket (Figure 4). We want to make sure that we don’t roll this gasket when we install it.

Figure 4

Now we’ll flip it over and install it. Now that we have our valve cover on, it doesn’t look like we rolled any gaskets. Let’s drop our bolts on in. Something to keep in mind is that most valve covers will have a torque sequence and a torque value that you have to hit, so you want to make sure you follow them.

The Mazda one is really weird, because we start in the middle and kind of work our way anti-clockwise, which is very different from how Volkswagen does it. However your car is, follow your manufacturer’s repair manual. I always like to start these bolts by hand, you may need to wiggle the valve cover just a little bit, but I like to start them by hand so that we know when we go to snug them down, we’re not going to cross thread them.

Then I like to just snug them down, usually with a power tool, but we’re not trying to send them home, just snug them up and that’s all. So, the torque on this valve cover is 43 to 78 in.-lbs. Be very certain that your torque wrench is set to inch-pounds, not foot-pounds.

I have mine set to 55 in.-lbs. After torquing them, I usually go around twice on valve covers, especially when it’s just a torque value, not a torque value plus a certain amount of turns (Figure 5). A couple will usually loosen up after you torque them all, and these are all super easy to get to, so it’s definitely worth it.

Figure 5

Now that we have our valve cover bolted down, we can put everything back where it goes, including our spark plug wires. We need to get our two bolts for the back bracket. For this back bracket, I feel like starting both bolts and then tightening them down is probably the way. Make sure you plug any connectors that you disconnected back in. As we start to wrap this up, I want to make sure that I replace the PCV valve.

So, valve covers like this are generally super simple to replace. Typically, the hardest part is actually getting to it and dealing with old hoses or wiring harnesses and things like that.

Also, you always want to make sure you check your work and be sure that you don’t have any oil leaks after you just fixed your oil leak, which I’ve had happen before! TS

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