Synthetic oil MPG boost since change

[swng]

Originally Posted by blacksan

I use synthetic in both engine and tranny. I short shift at low RPM and keep a real steady throttle at speed. When I changed the tranny fluid to synthetic I noticed how much smoother the synthetic was as I lost a discernible degree of engine breaking with the tranny. On my previous car (Subaru) I still had 75% brake pad material after 80K which is a result of my interstate commute and engine breaking with tranny. Does this help?

BTW, I change my filter at 5K and top off with a full fluid change at 20K with Amsoil synthetic in both motor and tranny.

Very sensible! The dealership has been offering to change my engine oil to synthetic oil for double the price of the regular mineral oil (about C$35 with regular and C$70 with synthetic oil in a basic routine service, plus tax, if I remember correctly). As I have all along been using the Yaris basically as a light duty workhorse car, not a heavy duty/sports car, I have chosen to stay with regular i.e. mineral oil. Since I need to change the oil about every six months, I think considering my rate of fuel consumption, even with the noticeable better fuel economy to be expected, there is little chance that the synthetic oil can pay for itself. Now that you say that synthetic oil improves smoothness (I admit I am slighty surprised), which I presume will render the driving more pleasurable, may be I should give synthetic oil a try.
Remember, the Fuel Economy thread always welcomes sucessful fuel savers like you to share their reasons for their fine achievements.