I would test your mechanics theory by doing another oil change, this
time making sure I drained the cooler and changed the filter (which I
always do since my cooler has a drain cap, and like the others who
have stated so, my oil stays so clean for several hours after a change
that it is hard to read the dipstick in certain light situations). See
what happens then. You can keep the oil you have now and use it a
quart at a time in the near future if all is OK.
Also, the Cardinal club has a technical page (members only), that
shows an owner who made a small slim light from a flashlight bulb and
wire that was small enough to fit thru the spark plug hole. If you
remove both plugs, and slide the light in one hole and look through
the other, you can see if the cylinder is glazed or if there is a
major problem. Not as good as borescope, but better than nothing.
As a matter of fact, I put a reworked cylinder on #4 of my O-360
8 hrs ago. I am still running the Mineral break in oil, and the oil is
still almost clear and it is hard to read the stick, even though I
don't have fully seated rings yet on one ccylinder (chrome cylinder),
and I did not change the filter when I put the break in oil in since I
only do that every other oil change, and I am going to change back to
AD at 10 hours when I will change the filter, drain the cooler, and
add Aeroshell 15W-50.
I have had a forced landing, and can tell you from experience,
you must do whatever you need to, to prevent having one yourself.
Keeping that fan turning matters as much as anything there is. I was
lucky with no injury or damage. I am sure my next time I will not be
so fortunate. Know what you are dealing with!!

Regards,
Bud

On Jan 29, 11:49 am, "Dan Luke" wrote:
wrote:
Definitely have an A&P borescope that engine. Broken ring maybe.Talked to my mechanic this morning. He said not to worry; the dirty oil is
from the oil cooler and its plumbing, which don't get drained when the oil is
changed.

He said I would have noticed this before if I had ever checked it two hours
after a change. Since I check the oil before every flight, it seems I would
have noticed the oil's turning black this soon before.

Should I pay to have the cylinders 'scoped?

--
Dan
C-172RG at BFM