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    Super Moderator LarrBeard's Avatar
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    Oil Bath Air Cleaners 101

    It is funny how a lot of us end up talking about the same subject at the same time. The discussion of this week has been oil bath air cleaners. Oil bath air cleaners, Donaldson oil bath air cleaners in particular, are an item that look simple, but have a lot of sophistication once we start looking at them.

    Donaldson air cleaners rely on the fact that dirt has weight and anything with weight has inertia. We dont think of dust and grit as having inertia, but particles of crud tend to keep moving in the same direction just like everything else. Donaldson air cleaners take advantage of this to make dirty, gritty, dusty air into something that our Jeep carburetors will use and not grind up the innards of our engines. In fact, a guy named Dyson is making a lot of money selling vacuum cleaners that use this same principle.

    The oil bath air cleaner consists of a canister having two concentric cylinders inside it. Dirty air enters the cleaner through a number of holes in the side of the outer canister. In many of the civilian Jeep applications, these holes are up against the wheel well so that as little rain or other water as possible will get into the air stream. On the M38 and M151 military Jeeps, which go swimming on a regular basis, there is a water separator to make water entry less probable.

    Air enters the outer canister, it swirls around the inner metal cylinder and is drawn downward toward the bottom of the air cleaner. This cyclone action uses the inertia of the larger dust and grit particles to throw them against the wall of the outer cylinder and then lets them drop into the oil puddle in the bowl at the bottom of the filter. At the bottom of the outer cylinder, the air stream makes a 180 degree turn, heading upward into the inner chamber of the air cleaner. Once again, inertia comes into play. Most remaining dust and grit does not make the 180-degree turn and drops into the oil puddle.

    Now, the mostly clean air enters the inner canister where it goes through the steel wool, or whatever material, to the air cleaner outlet at the hose to the carburetor. This material acts again as a maze for remaining dust particles and provides acceptably clean air to the engine.

    Yep, its messy. But it has the advantage that it is a fail-safe design. Even if the oil bath at the bottom gets so full of dirt, dust and grit that it turns into a solid block of grease, the inertia action of the filter and the steel wool maze will still remove a bunch of dirt from the air stream. A paper filter is a fail unsafe device if it gets dirty the air stream is blocked and the engine quits. This is no big deal if you can run down to the parts store for a new Fram air filter, but if you are in West Waziristan BFE .. .

    And, once again, the CJ3 people have done a much better job of describing this that I can. Here is a link to find out everything you would ever want to know:

    http://www.cj3a.info/tech/aircleaner.html
    Last edited by LarrBeard; 08-25-2018 at 01:49 PM.

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