What is a valve cover gasket and how does it work?
Each cylinder head on your car’s engine has an aluminum or plastic valve cover bolted to it. Between this valve cover and the cylinder head, there is a gasket that keeps engine oil from leaking out. The valve cover bolts keep the gasket compressed, thus preventing leaks. Over time the gasket becomes brittle from the engine’s heat or the bolts loosen, creating an engine oil leak.
When to consider replacing a valve cover gasket?
Look for these signs of oil leakage at the valve cover gasket:
Oil seepage or dripping. Should the joint between the valve cover and the cylinder head fail, oil often becomes visible on the valve cover or cylinder heads. Usually, the oil will attract and hold dirt.
Oil accumulating inside the spark plug well. The spark plug tube seals are part of the valve cover sealing system. If the tube seals are leaking, you will see oil on the spark plugs or wires. The valve cover gasket and tube seals are all replaced at one time if either fails.
Oil leakage at the rubber grommets. The bolts holding the valve cover to the cylinder head sometimes have rubber grommet seals under the bolt heads. If these seals are leaking, you will see oil seepage around the bolt heads.
How do mechanics replace a valve cover gasket?
Remove engine cover. Some engines have plastic covers over the entire top. The plastic engine cover is removed to access the valve cover(s).
Remove components. On 4 cylinder engines, the valve cover is usually readily accessed once any electrical components and emission control tubing are removed, plus any accelerator linkages that might be in the way. On 6 or 8 cylinder engines, depending on which valve cover gasket is leaking, removal of the air intake plenum might be required, as well as additional steps.
Remove valve cover. Once the valve cover(s) is accessed, the cover retaining bolts are removed and the cover pulled off. The valve cover sealing surface is checked with a straight edge to be sure the cover is flat and thus reusable.
Install new gasket. The new valve cover gasket is applied along with new rubber grommets under the retaining bolt heads. If there are spark plug tube seals, these are replaced as well. In some applications, oil resistant RTV (room temperature vulcanization) sealant must be applied to specific segments of the sealing surface, along with the new gasket, to ensure a complete and effective seal. The cover is bolted back on, using a calibrated inch pound torque wrench, and all other components are restored to their original position.
Check for leaks. Finally, the car engine is run and a visual check is made for oil leaks.
Is it safe to drive with a valve cover gasket problem?
Yes, as long as the amount of oil leaking is small, and there is no leak onto hot engine parts such as the exhaust manifold, it is safe to drive your car until you have an opportunity to fix it. If you notice oil leaking on to the ground beneath your car after it is parked, you do not have a small leak, and it needs to be found and repaired as soon as possible. Any leak, of course, means your oil level is dropping as you drive the car. If you have a leak, be sure to check your oil more frequently than usual so you do not run low on oil and damage the engine.
When replacing a valve cover gasket keep in mind:
The mechanical components of a car engine will typically outlive the gaskets used to seal the engine. However, many of these gaskets, including the valve cover gaskets, are relatively easy to replace. Never add stop leak type products to engine oil or other vehicle fluids. Not only are these materials not approved or specified by the original equipment manufacturers, but they also can create additional problems that may be costly to repair. Often, if a car is old enough to have a valve cover oil leak, there will be oil leaks elsewhere on the engine, so you should request a complete leak inspection. It may be more cost effective to repair multiple leaks during one service call. Often, the PCV (Positive Crankcase Ventilation) valve is inserted into a rubber grommet in one of the valve covers. An old rubber grommet is a potential leak source, as well as connections to the PCV valve. These components should be inspected and considered for replacement while there is access to the valve cover.