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K&N oil - was 84 4000S Quattro Questions

Jack Rich wrote:
> That's the whole principle of operation of the K&N, is that 
> the dirt sticks to the oil. Too much dirt will mean not enough 
> oil to stick to any more dirt, but IMO no dirt means sticky 
> fibers, not shrunken dry ones.

Yes, the oil is there to catch the dirt, but more dirt is 
actually a good thing for a K&N, up to a point. (The 
instructions say so!)

The air passages through a paper filter are roughly the same 
size throughout. They work on the simple principle that any 
particles that are bigger than the air passages will get caught. 
The problem is that once a particle gets caught, it's now 
blocking that passage, so there is less air flow through the 
filter. Eventually the air flow capacity of the filter becomes 
so low that it needs to be replaced.

K&N filters (along with all other oiled fiber filters) work on 
a different principle. The air passages through the fibers are 
not consistently sized. Therefore, they have some passages that 
are much bigger than the passages in paper elements. However, 
since none of the pathways are straight through the medium (air 
has to twist and turn through the passages), Most particles 
will be forced to bump into the fibers along the way. The oil 
is there to make the fibers sticky so that the particles won't 
just bounce off and continue into the engine. As the particles 
get stuck to the filter, they absorb some of the oil and become 
sticky just like the filter media. They also help to make the 
air passages more crooked, thereby making it harder for 
particles to pass though without hitting something sticky.

So, in theory, the K&N can flow more air (bigger passages) 
while still catching the bad stuff. In reality, you're probably 
giving up some filtering ability for that extra flow and 
extended service interval, at least until the filter gets a 
little dirty.

Eric Renneisen
'90 CQ 20V  -  my 'racing-iron'  ;^)
Chattanooga, TN