How to Diagnose a Leaking Valve Cover Gasket
One of the easiest things to diagnose on your engine is a leaking valve cover gasket. The most obvious symptom of a valve cover gasket problem is when you open your hood and see oil all over your engine. When the engine is running, you may even see smoke coming off the exhaust manifolds, and it will stink like burnt oil. That is the most obvious way to tell if the valve cover gasket is leaking on your engine, because it is letting oil run down the side of your engine or all over the top of it, coating everything with oil. Be careful though; sometimes valve cover gasket leaks can be hard to diagnose, and can cause different symptoms with how your engine performs. Here are some of the less obvious signs of valve cover gasket leaks, and how you can diagnose them.
If you have an engine that has the spark plugs that go down into the top of the cylinder head, right in the middle of the engine on top), then you need to be aware of any leaks from the valve cover seals that allow oil to get down in the hole with the spark plug. If the spark plug body is sitting in oil, it will not let the heat dissipate from the spark plug good enough, and the spark plug will be damaged. This will cause a cylinder to misfire (not work) and the engine might run rough either while idling, or only when trying to accelerate. The “check engine” warning light should turn on, and flash at you. When you have the codes read, you will know which cylinder to look at. Then you can expose the spark plug, and see if any oil has been allowed to seep down in there with the spark plug. If it has, then you know that the valve cover seals were the cause of the problem. If this happens to you, then you should also know that the oil will actually eat the rubber boot that protects the terminal on top of the spark plug, so it will also need to be changed along with the damaged spark plug. If you try to skip changing any of these things, the misfire will not go away.
Another way that valve cover gasket leaks can cause the engine to run poorly is since the crankcase also feeds air into the cylinders to be burned, if there is a leaking gasket, then your car’s engine can interpret that as a vacuum leak. To diagnose a possible vacuum leak from a valve cover, you would use the other popular methods for finding vacuum leaks, such as spraying engine cleaner around the area, smoke testing the system with shop equipment, and even listening with a stethoscope (or a short piece of garden hose, if you prefer the shade tree method). When you find the leak with the engine cleaner spray, the engine will speed up a couple hundred RPM, not much but enough to notice. If you are in a shop and use the smoke test machine, then you will see it right away from the smoke that starts bellowing out of the side of the engine. Finally, if you are hunting for vacuum leaks with the stethoscope, then you will hear an unmistakable hissing sound from the air that is being sucked into the engine through the leak.
As you can see there are some obvious and not-so-obvious ways that the valve cover gaskets on your engine can be leaking. How to diagnose each one of them involves a different approach, but you should be confident enough to know that now you have enough knowledge to be able to diagnose any valve cover gasket leak that you ever come across.
