See Figures 1 and 2
The PCV valve, which is the heart of the positive crankcase ventilation system, should be changed every 15,000 miles. The main thing to keep in mind is that the valve should be free of dirt and residue and should be in working order. As long as the valve is kept clean and is not showing signs of becoming damaged or gummed up, it should perform its function properly. When the valve cannot be cleaned sufficiently or becomes sticky and will not operate freely, it should be replaced.
The PCV filter, which is located at the air filter housing on the six-cylinder models, should be checked and cleaned every 15,000 miles. Just blow out the screen with compressed air in the reverse direction of the normal air flow. Check to see that the screen forms a good seal around the edges of the air cleaner housing so no dirt can pass. If the screen is torn or clogged, or it is seated improperly and cannot be repaired, replace it.
The PCV valve is located in the right valve cover on the 6-225; in the intake manifold between number 2 and 3 cylinders on the F-Head; in the intake manifold behind the carburetor on the 350 V8 and all American Motors V8s; and on the valve rocker cover on the 6-232 engine.