I just filled my 05 prius with octane 91. After reading some threads, I am concerned. Will just one tank of gas with 91 octane affect my engine or its mpg performance? It is very cold right now. 23 F. By Sunday it will go down to 9F.
You should be ok. Most Prius owners here will say that it is just a waste of money to pay extra for high octane. Since I got my Prius, I just put in 87 octane and it runs fine.
read the manual, your engine will probably knock with 85 octane, especially going uphill. your engine will not knock with 87 octane, putting higher octane will decrease mpg and will not "clean out the engine" and will not "treat your car to something nice" your engine may or may not knock with 86 octane, depends on quality. My $0.02 advice: add quality gas like Mobil, Chevron or Shell, almost all of these stations don't even have 85 or 86 octane, and use 87 octane
