Since many factors can indicate a poor valve stem seal, it's important that you investigate rather than always relying on signs. If you have the proper training and qualifications, go ahead and start your inspection. Otherwise, rely on the guidance of an expert.
Step1
Open the hood and check the oil level of the machine using the dipstick. Is it significantly lower after a similar amount of use compared to other times? You can also check for excess clearance between the valve stem and the guides. Leaks are an obvious sign that there are problems with the valve stem seal - but these problems are not always present, even if the seal fails.
Step 2
Start the engine and observe the exhaust. Is there a lot of smoke coming out of the pipes and is it a bluish-gray hue? If so, the engine is burning the leaking oil - which is why you may not see any leaks under the hood.
Step 3
Listen for strange noises such as rattling or knocking sounds when the engine is idling. Any unusual sound could indicate a valve problem.
Step 4
Check for engine and error lights that could indicate a problem. You can connect the machine to a diagnostic reader to scan for different error codes. For example, valve seal and valve guidance problems will be interpreted as specific codes, so refer to the user manual for help.
Step 5
If the situation gets worse, you will need to disassemble the engine and inspect the valve stem seals and other components. It may be best to rely on a professional for this step to ensure that more parts are not damaged during the process. You or a specialist should check for dented, cracked, broken or deteriorated valve seals.
In the long run, valve stem seals can be affordable to replace because new seals can prevent more serious engine damage.
Valve cover gasket leakage and repair 