Hi,

There is only ONE way to get ALL the crud out: tear down the engine and
clean all the parts!

Short of that, there will ALWAYS be a certain amount of crud deposited
somewhere in the engine. The places it's going to build up most,
assuming regular oil changes, will usually be benign "nooks and
crannies" where oil splashes and lands, then sits w/o being able to
circulate quickly. With MOST engines, this is NOT a problem (however,
there ARE some engine designs that are problematic, but they're
problematic REGARDLESS of the oil being used. One case in point being
the infamous Toyota "sludge engines." Not to single out Toyota--many
other mfrs have had one or more of these "problem child" engines.) As a
general rule, those places that have either pressurized oil flow, or a
lot of oil flowing over them all the time, like return galleries, will
show the least buildup of varnish or other crud. That's simple enough to
see in a teardown.

What does oil analysis do for you in this regard? It simply tells you
WHEN you need change your oil because it's reached the maximum level of
contamination it can handle w/o causing "excessive" wear or damage to
your engine. I say "excessive" because the engineers design a certain
amount in when determining THEIR idea of the life expectancy of the
engine. By changing oil and filters far more frequently than suggested
by the owners manual, we MAY be able to cut the wear factor far below
the design level. And then again, we may NOT. This is ONE of the reasons
you will probably see far more of the "high mileage" engine reports (a
quarter million miles or more is a number that sticks in my mind) are
from guys who change at more frequent intervals. But the frequency of
oil changes is only one of many factors in engine longevity, so it can't
be pointed to as THE reason a particular engine lasted a certain number
of miles.

So while the best way to achieve dependable oil analysis figures is
probably to start with a "new" engine (crate new or rebuild new) and get
a baseline figure, then have a series of oil analyses done at differing
intervals to determine what the best "average" interval is, you can
start at any point and at least have a baseline figure to use to
estimate your engine's condition. At first, while the engine's wearing
in, certain numbers will be high, then they'll usually stabilize, so you
can tell how far from a given number you've "strayed" which CAN be a
useful diagnostic tool if you're running a fleet. For the individual
owner, it's probably more a "feel good" thing, since most of us aren't
going to stop what we're doing and tear apart an engine when we see a
"high" number for say, a bearing material, indicating bearing wear.
We're going to watch the oil pressure gauge, and figure as long as it's
ok, that bearing hasn't worn badly enough to worry about.

This is why I suggested you siphon the "clean" oil off your specimen and
have it analyzed! Most of the contaminants that cause wear, the
particulates, will have settled out and won't be present in that "clean"
sample. Other items, such as metals, may or may not still be present.
But the analysis figures will tell you "change" or "keep" even so.

Another thing oil analysis will do is tell you what you're LOOKING at is
anything, or nothing, in the grand scheme of things. One of the things
your oil does is "clean" in the sense it carries crud to the filter to
be caught and held for disposal at the next change. One of the criteria
the engineers look at is the "size" of the crud, measured in microns (1
micron = .000001 m = .000039 in), and there are ranges to be concerned
with, ranges not to worry about. Most sources you can easily find
suggest most of the engine wear is caused by particles in the 5-20
micron range. A majority of oil filters on the market do VERY well at
removing crud above 20 microns, some do a pretty good job in the 10-20
micron range (brand and model CAN'T predict this! Only testing does--one
catalog number may be excellent, another barely passable), few do so
well below 10 microns or so. Why not? Engineers must balance flow and
pressure against efficiency. They CAN filter out much tinier stuff, but
then you'd be changing your filter every few hundred miles when it
clogged, and who knows how long your engine would last w/ the reduced
flow? So there's a balancing act involved.

Now to take this further, we have bypass filtration. A bypass filter CAN
get out extremely tiny junk but it can't flow much. So I'm gonna
illustrate why your "visual" estimation of how good a job your oil is
doing can be flawed.

Years ago the Frantz people introduced bypass filtration to the masses
with the "toilet paper" filter. The people selling these filters had a
neat visual aid they used to show people how well their unit worked.
They had a test bench set up with a container of clean oil, a pump, a
full flow filter and a bypass filter. There was a switch to put the
bypass filter in the loop or take it out.

They would start the machine, and you could watch the oil go thru the
full flow filter and the bypass filter. Since it was clean oil, it
wasn't an impressive sight at first. But then they would isolate the
bypass filter, and introduce a bit of carbon black to the "clean" oil.
Instantly it would turn jet black! And as it circulated thru the full
flow filter, there was NO change in color. Then they'd turn on the
bypass filter, and in a couple of minutes, the oil was back to being
"clean" again.

So the first thing that would go thru one's mind as they watched this
was "that oil is filthy" followed by "my oil filter's not doing much of
a job" and, the salesman hoped, you finished with "I'll buy one!"

But as I mentioned before, there's more than meets the eye! Carbon black
is LESS than 1 micron in size. So it's NOT a player in the wear
equations! But it certainly makes the oil LOOK bad! And, using your
visual "settling rate" estimation, it would stay "in suspension" for an
extremely long time simply because the mass of the particles is so low
it takes "forever" to settle out. Oil analysis would help you determine
if you're looking at actual wear particles, or just "carbon black" type
contaminants! One would dictate it's time to change your oil, the other
is strictly "fuggedaboutit" territory.

So "you pays your money, you makes your choices, and you takes your
chances!" IF you're blessed with the resources to take two IDENTICAL
engines, and run them under IDENTICAL conditions side by side where the
ONLY variable being changed is the oil being used, change intervals,
filter, or some other item, you can come up with decent data on what's
"best." Since the mfrs DO have these resources, and DON'T recommend any
particular oils or filters as a result of their testing, there should be
a lesson in there for us mere mortals who have to work hard just to have
one or two vehicles to drive! Otherwise, we're just arguing how many
angels can dance on the head of a pin... and that's why the man insisted
on "Show me your numbers...!"

Rick