As a heavy duty mechanic i have seen the results of synthetic and dino oil up close. If you are going to make the switch I recommend letting the oil drain for at least a day. Any mixture of the two oil types will result in the internal parts and oil galleries becoming plugged with sludge and blocking or limiting propper oil flow.
IMO the only time to switch between the two oil types is after (or during) a rebuild to eliminate any cross contamination
IMO the only time to switch between the two oil types is after (or during) a rebuild to eliminate any cross contamination