When should I start using synthetic oil??

[SilverGlow]

Originally Posted by UTVitz

I tried Valvoline Synthetic in my '08 Yaris for a month-it did not like it one bit. From a noticably noisier engine to a significant drop in my MPG (I always run in the 40's with it till I tried synthetic and it droped into the high 30's for the entire time the oil was in it). I went back to conventional valvoline after a month and suddenly the engine seemed more dampened in operating noise and my MPG went right back up to 43. This is only my experience with it and I've read a few others that noticed this same effect with their Yaris.

Hmmm, when I used Valvoline Syn my MPG went up 1.5 MPG over using conventional Valvoline, both at 5w-30.

I think your change in MPG is caused by some other reason. The difference in MPG between ANY oil brand is 2% or less. The increase in MPG when using the "best" synthetics is just 1% to 2% over ANY conventional.