Valve stem seals are small seals that are fitted around the valve stems in the cylinder head of an engine. They help to prevent oil from entering the combustion chamber, which can cause excessive smoke and a decrease in engine performance. Valve stem seals will wear over time and may need to be replaced if the engine begins to smoke excessively.

A pressure test is a type of test that is performed on a cooling system to help identify any leaks or other issues. The system is pressurized with air or a special tool, and any leaks will cause a drop in pressure. This can help to pinpoint the location of the leak, which can then be repaired. A pressure test is often performed when an engine is overheating or when there are other cooling system issues that cannot be identified through visual inspection.