I'm a new owner too, but I've learned very quickly to trust mechanics about
as far as I can throw them with my left arm.

Like many other things in aviation, there are few aboslute answers, only
statistics. Maybe 9/10 oil-analysis problems could be picked up by visual
inspection. Maybe 95/100 could be predicted just fine with 100 hour analysis
instead of every 50. Adjust these numbers to your heart's content, but there
is always a chance that a 50-hour analysis will save your butt. Considering
that this costs less than a dollar per hour, I'll take it.

Some guys change their oil every 25 hours for this reason. I go 50 because
plenty of people do and don't have any problems. But if I was flying low IFR
regularly, I'd probably switch.

Most of what "A lot of people on the field" know has to be taken with a
grain of salt, a bigger one if you're a newbie and don't have a good BS
detector. Half of what people in aviation "know" is more voodoo than
scientific fact, especially in GA where the training is so variable. Hell,
go out in the sticks somewhere and you'll probably find plenty of guys who
think oil analysis is what you do when the stuff starts spraying on the
windshield. If you're flying in a Cub and surrounded by pumpkin patches I
suppose that might be a reasonable attitude.

Best,
-cwk.

"Bob Fry" wrote in message
...
"Don Gourlay" writes:

We used Blackstone for a couple of years. They alerted us to the fact
that
the aluminum content had shot up. Ended up doing a top overhaul.
Previously
the leak down tests were ok. We had heard this can change quicky which
it
did. The analyiss was the trigger. AME said things would be been fine
for
about another 100 hours but we did the top anyway.

A lot of people on the field laughed at doing the analysis every oil
change.

Don--

I have an Aircoupe with a C-90 engine. First airplane owned so I'm
still learning. OK, my mechanic is skeptical of lab analyses, and
prefers examining the oil and filter after each change. Best would be
to do both, but my question to you and others is--

If you could only do one thing: either lab analysis of oil after each
change, or your own visual examination of oil and filter after each
change, which would you do?

In your above scenario where the lab alerted you to a problem, would
you have noticed the problem by doing a visual inspection of oil and
filter--like seeing metal particles?