Interesting post found on oil filter stuff...

[Jerry Bransford]

Rich Hampel on the rec.autos.makers.jeep+willys newsgroup just posted the below response to a statement that I copied to the bottom of this post... I don't know if what he says is 100% true or not but it was interesting reading anyway...

"No no no no no

Its true that a resinated paper removes ~25 micrometer particles (at
about 98% efficiency) but such paper also has removal efficiency at the
submicronic range but to a few% removal capacity (called a 'beta curve'
in filter-geek speak). Since the oil RECIRCULATES constantly through
the filter media the reduction of particle size continues and will
'level-out' at some predetermined level (probably at about 0.5- 1,0?M).
A filter also becomes more efficient at removal size as more debris is
captured (clogging the 'holes' and leaving smaller flow paths).

In a perfect world one would have a differential pressure gage mounted
across the oil filter to indicate when to change - when the
differential pressure starts to quickly increase - indicating that the
volumetric flow is declining.


It is possible to re-condition sump oil onboard using a 'depth-media'
filtration using the same cellulose filter media but requires a very
LARGE filter set ..... but the surfactants and other additives would
have to be replaced. Oil never 'wears out' it becomes contaminated
with the byproducts of combustion: acids, metal particulate, etc. and
if you add back the needed 'chemicals' to particulate free oil you will
never have to change .... as do many truck fleet operations.

Moral of the story: dont worry about the retention rating of a
recirculation filter; just put on the LARGEST filter you can find.
The LARGEST will have the least resistance to flow and will allow
faster total volume recirculation throughput, the faster throughput
allowing exponentially greater opportunity of capture of much smaller
(submicronic) particles. In engineering geek-speak all you have to
do is filter to a level of 1/5 the size of the smallest orfice or
clearance that you're trying to protect ..... and everything will be
FINE .... This 1/5th 'yardstick' will prevent the particles from
agglomerating and 'bridging' thus scouring the clearance or blocking
the orfice. ( The 1/5 rule also applies to 'single pass'
filtration.such as fuel systems)"

(end of Rich's response to the below post)

I have had the opportunity to study quite a lot of closely held
> > oil/filter/wear information. Here's the basics:
> >
> > Keeping oil clean is the primary goal. What is 'clean'? The primary
> > component of 'clean' is particulate loading and particulate size. Your
> > normal paper oil filter filters out most of the particulates 25 microns and
> > larger. That's 0.001 inches. The smaller chunks keep circulating. Think
> > about a low viscosity slurry of oil and rubbing compound.

[Joe Dillard]

Maybe I'm just a nut.....I simply change my oil & filters somewhere between the 3-5K mile area & don't give it much more thought. In my '88 Toyota Tercel speed demon - it gets the el' cheepo Walmart oil & Fram filters. I can't see spending much $ on a 17 year old A-B junker with 220K+ miles.

In my POS YJ, it actually gets changed more frequently due to the low miles it sees yearly. Plus, it's old.