Gaskets are hard-working soldiers when it comes to sealing engines, receiving great abuse but usually never being recognized for their efforts. One of the most important gaskets that protects cylinder head hardware from components and prevents oil from escaping the motor is the valve cover gasket. Most valve cover gaskets are made of plastic or cork and serve as a seal between the cylinder head and the head itself.

Symptoms of bad bonnet gaskets

Dirty valve covers and visible oil leaks
Low engine oil level
Smell of burning oil
Engine misfire and rough idle
Instrument panel warning light
Smoke coming from the engine

Although the valve cover gasket is well protected from the top and bottom, it is very fragile and can be easily damaged from the sides. After a period of time, the gasket can become brittle and can break from exposure to dirt, debris, heat and other elements. When this happens, the gasket can lose its integrity and leak, potentially leading to cosmetic problems such as oil leaks, or drivability problems and reduced engine performance. A bad valve cover gasket can lead to complete engine failure if not replaced in a timely manner by an ASE certified mechanic.

1. Oil burning smell
When the valve cover gasket is squeezed, worn or cracked, the compression oil under the valve cover will find a way to escape. When this happens while the engine is running, excess oil will drip onto the cylinder head, fuel inlet or in some cases the exhaust pipe. These are hot components that burn oil and produce an easily recognizable burning oil odor. If you smell burning oil, contact a professional mechanic so they can properly diagnose the cause of the leak and fix the problem.

2. Dirty valve covers leak oil
During most oil changes, the technician will check the valve cover to see if there is any oil leaking from the valve cover gasket. The fastest indication of this problem is a dirty valve cover/cylinder head. The oil will collect dirt and debris under the hood and will appear to be "caked" on the valve cover or cylinder head. If you change the oil, or look under the hood and find a dirty valve cover, it is probably due to a damaged valve cover gasket.

3. Engine oil is low
When oil leaks from the valve cover gasket, it leaves the oil pan. When this happens frequently, it can cause the engine oil light to appear on your dashboard. If the engine oil level is low, it will reduce its ability to properly lubricate the internal parts of the engine. This can build up excessive heat inside the motor and cause serious engine damage. If you notice the engine oil light coming on at any time, do not delay service or assume it will turn off on its own. Contact a qualified mechanic to diagnose the problem and repair the cause of the oil leak.

4. Engine runs rough and misfires
Sometimes when oil leaks from the valve cover gasket, it leaks all the way into the spark plug well and eventually seeps into the spark plug tube. This will cause misfires or reduce engine performance. It can also cause a fire under your hood if not repaired.

Conclusion

Even if your valve cover gasket fails, you can continue to drive. However, you want to make sure that any oil leaks are small and that there should be no oil hitting any hot engine parts.
As mentioned earlier, oil on hot engine parts may produce fumes and the smell of burning oil. Just because your vehicle is drivable doesn't mean you should ignore any problem and fix it as soon as possible.
You may experience low oil levels, check engine lights and other problems when you find a gasket leak. Therefore, the more you put it off, the more likely it is that your car will fail completely.
While replacing the valve cover gasket may seem like a simple task, this gasket is often hidden behind many engine components.
Therefore, if you are unfamiliar with the engine configuration or have never replaced an engine part before, the task can quickly become tiresome.
In these cases, you want the help of a skilled mechanic who can help you get the job done quickly. In the end, you can rest easy and not worry about the details.

Common Problems

Can you drive a vehicle with a leaking valve cover?
Yes, you can drive a vehicle with a leaking valve cover as long as the amount of oil leaking from the gasket is minimal and your oil does not spill onto hot engine parts such as the exhaust manifold and pipes. If this is the case, it is quite safe to drive the car until you can see a repair store or repair it yourself.

Is a leaking bonnet gasket a concern?
Is there an obvious valve cover leak? When a bonnet gasket shrinks over time due to high engine temperatures, it loses effectiveness and leaks, usually resulting in oil leaks, reduced engine performance and drivability problems. Leaking bonnet gaskets can lead to serious engine failure if not repaired in a timely manner.

When do I need to replace my valve cover gasket?
Because your valve cover gasket is made of rubber, it shrinks and becomes brittle when your engine overheats, which is the most typical cause of oil leaks under the valve cover. 

When is the right time to replace the valve cover gasket?
Your valve cover gasket requires no maintenance. It must just be a case of it shrinking or leaking. However, valve cover gaskets are primarily replaced when extensive engine maintenance is performed.

How long can you drive if the valve cover leaks?
It is usually prudent to avoid using your vehicle if it has any oil leaks. Short trips within the city or less than 10 miles are not as harmful as driving with any oil leaks before the oil level drops. Avoid driving your vehicle if the oil leak is severe.

Can a leaking bonnet gasket cause smoke?
When oil leaks out of a valve cover gasket, it runs down the exhaust manifold or exhaust pipe. When your engine heats up at idle or while driving, the exhaust gases and oil will be heated. When this happens, you will notice white smoke coming from under the hood.