Lots of factors to consider. What climate the plane is based in and flies to is probably my biggest consideration. I like straight weight oils (W100) if the ambient temp isn’t below about 45 deg F or so. If you preheat the engine, that can go lower. The multi vis oils seem really good if you fly in a variety of temps or sustained cold temps. One winter, i kept straight weight W100 in a Lycoming but made very sure the oil was well preheated every time before start. Not sure this is a good idea, though. switching to multi vis and preheat is probably better. The W80 is pretty thick when it’s cold, too, so preheating that is a good idea.
Lycoming recommends the anti scuff additive, so if using Aeroshell oil, use the 100 plus or the 15/50. those contain the additive. straight W100 or W 80 does not, so you have to add it. if using Phillips XC, use the Victory one with the additive. All of these are the ashless dispersant oils. straight mineral oils for break in are a different thing.
I use Philips X/C 20w/50 in my IO550 Continental plus Camguard. Any plane that doesn’t fly frequently is at risk of internal corrosion. the camguard helps the oil “stick” to internal metal parts long after the engine has cooled. it definitely makes a difference.
Note that the Lycoming additive and Camguard are not the same thing. the former is an anti scuff agent and the latter is for long term corrosion protection. I have no experience combining both, but people do.
My IO550 Continental runs cool in the winter, so i have to block off part of the oil cooler to keep the oil temps up. very comfortable with the multi vis oil in this plane. My 0-235 Lycoming has no oil cooler and runs in the upper range of oil temps, so i don’t worry much about using W100 in winter assuming it’s preheated.
Final thought to this rambling post - in my experience, the amount of oil either consumed or blown out the breather for a given engine can be different depending on the oil. I have reduced the oil consumption by changing brands. Multi vis tends to disappear faster. Also every engine has a sweet spot for oil quantity. very few like to be filled to capacity. i run 12 quart sump engines at 10 quarts. any more and it gets blown out the breather. for six quart sumps, 5 seems to work. every engine seems to be different.
