Call me crazy but....

I've had syn in my 350 every since my first 2500K change. Most recently I had Royal Purple. Over the next 12500 miles my gas mileage averaged about 20 to 20.5 religiously. That's with pretty aggressive driving at times. Recently (a few hundred miles ago) I had my car fixed for the VVTI cold start noise. Electronics were reset during the service so the average oil readings were reset also. I had them do a 15K service on it while it was in the shop. Of course, unless I specify otherwise, they put reconditioned regular dino in it. I didn't ask for synthetic (I forgot). Since I got my car back the average mileage went from 17 and is hovering at about 18.5 right now. Same for tank average and total average. Now call me crazy but could it be that syn actually DOES give you better gas mileage? Roughly 2 miles per gallon is significant. I haven't run the numbers but over a 5K oil interval 2 mpg is significantly more savings than the premium spent on syn oil... I always just poo pooed the claims of people like Royal Purple about improved fuel economy but I think I stand corrected. There is something to it.

 

A low viscosity synthetic oil should give better mileage. Just remember we're talking a little gain and each brand will differ. The best safe mileage viscosity for the 3.5 would be 0w-20 synthetic.

Koz

 

It's not the syn oil, it was the service ! When you take your car in to the dealership service dept, they reset the ECU (or something similar), I experienced the exact same thing on my comp 5k service. Prior to the service, I was avg 22-23 mpg each tankful, immediately following the service my mpg dropped to 20 while my commute, driving style, gas type, etc was unchanged. After about 2,500 miles, the mileage crept back up to 22-23, where it is now. I'm convinced that the techs reset something and it took about 8 weeks for the IS to re-learn my driving habits . . .