Type of oil

99 1.8T passat. I am using 5w 30 Castrol oil regular. I have been advised recently to use synthetic oil because the molecules are smaller in synthetic. Should I change type of oil next time, or is is O.K. to keep using same oil; and if I change, what do I need to do with the engine because as I understand, the two oils are incompatible (i.e. flush it, run with automatic transmision oil for couple days, etc.)?

I read on other forums that is better to use synthetic, and also they say it's not necessary to flush the engine, but I heard from my mechanic that it good to drive with quart of transmission oil two days prior to oil change. It seems like it removes sludge from engine. Anyone advises?

99 1.8T passat. I am using 5w 30 Castrol oil regular. I have been advised recently to use synthetic oil because the molecules are smaller in synthetic. Should I change type of oil next time, or is is O.K. to keep using same oil; and if I change, what do I need to do with the engine because as I understand, the two oils are incompatible (i.e. flush it, run with automatic transmision oil for couple days, etc.)?

I'm curious; why do you use 5W-30?

Low weight--good for small engines. And synthetic so it goes into small holes and has high breakdown temperature--good for turbo.

5w-30 Castrol full synthetic.