An engine that’s burning oil spews obvious signs and signals. Clouds of smoke at startup or when getting on and off the throttle visually show where that quart of oil every 500 miles is going. If the dipstick is reading low and there’s no sign of oil smoke, suspect an oil leak. While the source of oil leaks can be hard to locate, a common and relatively easy to repair source is located where the valve cover meets the cylinder head. If oil is going missing and the area around and under the valve cover is soaked, then it could be time to replace the valve cover gasket.
Intake and exhaust valves open and close at rapid rates while the engine is running. This action makes for mechanical mayhem under the valve cover. This thrashing about creates and requires a hot oil shower for lubrication. The valve cover gasket sits between the engine and the valve cover and seals the oil inside. Time and many miles can dry out or crack the valve cover gasket. If the seal created by the valve cover and valve cover gasket loses its ability to contain all the oil flying around inside then oil will escape. Valve cover bolts can also work their way loose. Valve covers can also warp or crack.
Locating oil leak sources can be tricky. The telltale sign of a valve cover gasket that has lost its seal is an oil-covered valve cover or a burning oil smell when the engine is running. As oil leaks from a valve cover, it can contact a hot exhaust manifold and burn. Smoke can then waft into the cabin. Oil from a leaking valve cover can also travel down the back or side of an engine and mimic a leak from somewhere else, such as the rear main seal or oil pan. An inexpensive telescoping mirror can help locate otherwise hidden valve cover oil leaks. Start looking at the top and follow the oil trail. A valve cover can leak oil while the engine is running, but not while the engine is at rest. The action of the valves kicks around a lot of oil.
If a valve cover oil leak is suspected, monitor the oil level closely until the source of the oil leak can be found and repairs made. Running an engine low on oil can be a disastrously expensive mistake. A valve cover leak can get worse as engine revolutions increase. The action of the valvetrain makes for a bigger oil bath. At high revolutions the engine can spew a great deal of oil while in operation and leak very little at idle, or none at all while at rest. Replacing a valve cover gasket is fairly basic but the procedure varies by engine. The toughest part is usually getting to the valve cover itself.
Step 1: The first step may be the last step. Before tearing everything apart, first try gently cinching down the valve cover bolts or use a torque wrench. Over-tightening bolts will not stop bad gaskets from leaking. Aluminum valve covers can crack. Steel valve covers can warp. Monitor oil level after tightening. Move on to step two if oil is still leaking.
Step 2: Allow the engine to cool. Consult the service manual or instructions for valve cover removal. This car is turbocharged and had a fair amount of plumbing in the way. Remove throttle cables, spark plug brackets, PCV hoses and anything else in the way. Remove the valve cover bolts.
Step 3: Lift off the valve cover. Tapping with a rubber mallet can help loosen the valve cover’s grip. Be extremely careful not to drop anything into the engine. If a nut or bolt falls into the engine there will be a lot more work to do. Even an old newspaper tented over the engine can help stop this from happening.
Step 4: Remove the old valve cover gasket and install the new one. The valve cover shown here is cast aluminum and has a groove in which the gasket sits. If scraping is required, do not use metal scrapers on aluminum valve covers or cylinder heads. Use plastic to prevent leak-causing nicks. Also note the new grommets on valve cover bolts.
Step 5: Apply silicone only where required. Do not use silicone or sealer unless the service manual or gasket instructions say to use it. Clean all oil off all surfaces before applying silicone. Allow silicone to cure before starting engine.
Step 6: Install the valve cover with the new gasket and tighten bolts to the recommended torque. Valve cover bolts don’t require too much twist. A torque wrench and service manual will eliminate guesswork. Install everything you removed to get at the valve cover.