Do not use Sunflower oil if you can avoid it. It will oxidize much faster than Rapeseed, and it doesn't lubricate quite as well. It tastes lovely, tho.
I've said it before and I'll say it again; I set my oilers to maximum, and I run straight rapeseed oil you buy from the grocer. Have been doing so since 2010. It works just fine and has saved me far more in oil expenses than it has caused any issues with my bars and chains. It is also biodegradable and does not cause any health issues that petroleum oil can. I've made a lot of firewood and felled a lot of trees over the years, nearly all of it with ported saws and long bars. If you work in very hot conditions, or stump a lot of trees or mill, you may want something thicker, but in the UK and Ireland, I haven't had issues cutting in freezing weather and in temps above 32C. I'm usually far less happy than the saw is in that weather.
When I remove a bar to dress it, I flip it. I dress my bars and clean them out often depending on the conditions. Dressing bars is kind of like sharpening kitchen knives. If you use a light touch with a sharpening hone every time before you use the knife, it stays sharp and useful for a very long time. Abuse it, and the knife stops cutting worth a damn, becomes dangerous now that you have to actually use force to make it cut, and you have to bust out the stones and spend a long time putting the edge back on that knife afterwards. A chainsaw is like a knife this way; when tuned right, you should not have to use much pressure. The saw does all the work. Use a light touch and clean and redress your bar often, vs a heavy touch and rarely. And flip it, flip it good.
USGS test on rapeseed based bio oils:
https://www.fs.fed.us/eng/pubs/html/98511316/98511316.html
Croation Forestry Dept test showing rapeseed based bio oils can run cooler:
http://www.crojfe.com/site/assets/files/3945/stanovsky_83-90.pdf
The usual mess I make: