Your Mazda 6's PCV System is an important part of your vehicle's emission system. It helps remove moisture, which is a major contaminant from the oil. The engine heats and cools, causing condensation in which the engine oil additives will absorb the moisture. When there is an excess amount of moisture, it will eventually contaminate the metal parts of the engine, causing damage. The PCV Valve helps draw fumes out of the engine and also acts as a buffer against oil being drawn out. The PCV valve will show signs of moisture contamination with cloudy/milky film or water inside of it. If there is a plugged PCV valve, it will eventually cause engine problems as there may be sludge buildup which can lead to oil leaks.