How does it work?

Just out of curiosity can anyone explain to me how the oil bath actually filters the air? I tried to search for this but couldn't find what im looking for. The stock oil bath on my 59 cj5 (Donaldson?) has many small holes on the back center of the oil bath which im guessing is where the air comes in? then it goes into the SOS pad looking filter and goes into the motor? but the oil cup at the bottom, I don't see how it will filter being at the bottom. So basically can someone explain to me the cycle of how the air comes in and gets filtered before heading into the motor?

 

As best I can picture it, the air bubbles through the oil in the cup, which catches some of the dust and bugs. Then the oil vapor is sucked up and coats the metal wool, and I imagine catches more dust as the air passes through it, which is then constantly washed down into the cup.

I know it works when I see the sludge I clean out of the cup!


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From what I've seen, the air doesn't actually flow through the oil like the above diagram shows. The air takes a tight turn like it shows just above the oil surface. The air being light can make the turn, but the solid debris has more momentum, cannot make the turn, and gets thrown down into the oil. An oil bath filter is actually VERY free flowing for air flow, but the maintenance of them was too much vs. paper and they phased out as time went on. Oil bath is still highly superior for actually filtering the air and still allowing for ample airflow.

Here is what I have always learned/understood as the proper function of the oil bath:

 

The air is saturated with oil and it is heavier than normal cool air. So when the oil falls to the bottom it takes any larger particles with it. The down tube then recycles and it starts all over

IMO an oil bath filter is superior to modern ones for off road types of stuff but it is no where near with fine stuff

 

So that must be why when I bought my 59 cj5 and removed the oil pan. There was 1/2 inch of sand in there sitting at the bottom....

 

Yeah sand is a killer on oil bath types - the military used to put cheese cloth around the opening when the Jeeps were used in sand

 

Hi, chiming in here......so take me for example....if I am running 99% on road should I pull the oil bath and get me a K&N?

 

In truth you probably could but don't think you half to. On road the engine will last a long time with the oil bath, as is proven by the fact that so many are still driven with them.

If you live in an area that does not tend to have a lot of sand, like near the beaches I would stick with the oil bath, it looks cool and it works well if maintained. That is the other side of things of course, the K&N basically requires no attention