My car originally was filled with regular 5w30 oil from the dealer, and I now use synthetic, but when making the change for the first time I just flushed the old oil out without running that alcohol stuff through to clean it real good. I've been using synthetic now for over a year and have noticed no problems what so ever, but I remember reading that some sort of solvent MUST be flushed through before making the change for regular to syn. Is this true that it's a MUST? and what can be the side effects of not doing so?

 

No problem. You don't say what kind of synthetic, but the normal stuff (Mobil1? SynTec?) is compatible. Over a year? Changed oil more than once since then? That's even better. The few ounces that's left behind when you change doesn't hurt.

 

So solvent needed

No results from the change. You can go back and forth as you please

 

u can go from regular to synthetic with no problem, but its not wise to go from synthetic to regular.

 

may i ask why....i use the mobil 1 synthetic blend 10w30...how much of a difference do u think the full synthetic will make as in : engine performance,less drag....etc....thanks