Jeeper  Adventures Under the Hood  Jeeper

The PCV System

The PCV system is simple, and has nothing to do with the computer. A manifold vacuum fitting at the rear of the BBD pulls fresh air through the crankcase and out through the PCV valve into the intake manifold, where any vapors are burned instead of escaping to the atmosphere. This reduces pollution and helps prevent sludge buildup inside the engine.

In order for this system to work the crankcase must be sealed. Any leaks will interfere with proper operation, and if they are severe enough the result can be oil blowing back into the air cleaner.

To test the system, pull the breather tube from the rear of the air cleaner and plug a vacuum gauge into it. With the engine running, there should be 3 to 5 inches of vacuum within 15 seconds.
Any openings in the valve cover can allow oil to leak out, and air to leak in. Check for oil around the filler cap (not oil that you've spilled on it while trying to get some in the engine).

Check for oil around the PCV valve and its grommet.

Check for oil at the valve cover hold-down nuts, one at the front and one at the back of the valve cover. There is a grommet on the inside of the valve cover at both of these locations.

oil leaks
The oil filler cap at the front of the valve cover has a rubber gasket on it that should seal it. With age this gasket becomes hard, more like plastic than rubber, and can leak. A new cap is about $3.
oil fill cap

What can go wrong?

Replacing all of the items described is inexpensive and can be done in an afternoon. Besides allowing the PCV to work as designed, another benefit is that the top of the engine will stay clean. Remember that all CJs are at least 30 years old, and these parts don't last forever.

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