Dan, I guess a lot of things can contribute to rapid blackening of the oil,
but in all cases it will be because some black stuff is being added to the
oil, and there is some source of the black stuff. In a previous Lyc
TIO-540-S1AD, I had bad exhaust valve guides. Hot gases blew through the
sloppy guides and burned oil in the rocker box. There was lots of black
stuff in the rocker box, and oil and suspended black stuff drains from there
back into the engine.

For pix, see http://aviation.sprevost.net/Engine-Photos/Cyl-Nr-1.jpg and

http://aviation.sprevost.net/Engine-Photos/Cyl-Nr-2.jpg for a bad one and a
good one.

Compressions were good until the problem got really bad. Then valve springs
and anything else that gets in the way gets burned.

It is easy to see if you have this problem by opening the rocker boxes.

Stan



"Dan Luke" wrote in message
...

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