Ok. You own a private aircraft and you don't fly as much as you'd like to.
You probably don't even fly 50 hours a year. The average is much less.
You might only fly 10 hours a year!
How I do maintenance for infrequently-flown aircraft:
In the springtime, drain the oil. If you have a pressure screen, remove it
and rinse the contents out onto a white cloth with mineral spirits to get
rid of oil and carbon deposits. Take a picture and mail it to yourself, so
you can watch the trend over the years. If it looks like this, you're fucked:
Lycoming actually talks about how much metal is acceptable. I am not
making this up.
If you have an oil filter, pull it and cut it open with a can opener and do
the same thing as with the pressure screen. Unfold the filter, rinse it
out and look for metal. Take a picture of how much you got.
Oil analysis is a complete waste of time, IMHO. Spend a few minutes
and look at how much metal your engine is making, as described above.
Most people don't bother, which is weird.
It's springtime, so buy a cheap straight grade oil. W80 or W100, whatever
you want. Halve the number to get the SAE viscosity, btw. If you have a
four cylinder, add a pint of Camguard to 5 quarts oil, which is 1/11 pints
or 9%, which I like. Smell it on final. Mmmmmm.
If you're running a six cylinder with a slobber pot like me, I like to run the
mother full at 12 quarts, all the time, because I have a wet sump, which
is a really weird design decision. I add 11 quarts and two pints Camguard,
which is 2/23 or 8.7% .....MMMmmmm.
When winter comes on, oil change again. Same pressure screen or oil
filter dance. I hate oil filters, btw. Every time I buy an aircraft with one,
I get rid of it. Does not pass basic cost/benefit analysis.
Buy a cheap multigrade oil, like Philips X/C 20W50. You know. Cat piss,
but it's ashless dispersant. Add Camguard as above.
I am not a fan of Aeroshell 15W50 or the "plus" W100+ oils with the same
package. It is expensive, makes your engine leak, and does not inhibit
corrosion as well as Camguard. You are better off buying a cheap oil,
and making it a very expensive oil with Camguard, which is what it was
developed for, but the suits shut it down.
TL;dr
For private aircraft, I do two oil changes a year. Straight grade in the summer,
multi-grade in the winter, as much Camguard as your wallet can stand. Spruce
sells it in four-pint packages.