Does anyone know how I can get to Sile and back from Istanbul's Asian side? Want to leave around noon or early morning and return late evening.

139 or 139a from Harem (near Uskudar) but dont ask me exactly where from!! The 139 appears to be much more frequent and stops in Şile, whereas the 139A goes on to Ağva.
Good luck!

You don't have to go all the way to Harem to pick up the bus, you can also catch it at the Göztepe Bridge on E-5. However, you'll be more likely to find a seat if you get on at the first stop. It's likely to be wicked crowded no matter what.

Here's the info on the 139 bus route. You can also find the times by clicking on 'Schedule'
http://www.iett.gov.tr/en/saat/harekets ... nDetay.x=4

IETT is in English as well so you may want to aquaint yourself with this site for all your transportation questions.