First Fill-Up used 91 instead of 85

should be fine...the only thing I've heard my Bentley maintenance guide for Gen2 says premium could be hard starting, but nobody has ever complained about.

PS- Reg is 87 except at high altitude

 

You will be fine. I have run 93 grade a hand full of times in my Cs engine. Nothing different.

 

The worst thing is that the higher fuel price caused a couple dollars to permanently vanish from your wallet. Compared to that, everything else is minor.

 

I use 91 only, no problems.

 

Why ??? unless that is cheaper in you corners

There are numerous thread here not only explaining why it has no benefit, but also taking measurement to prove it.

The engine designed to a max compression and that is what needs to be matched by the fuel properties.. in theory the atkinson engine could increase the compression from the working pre-set .. but it DOESN't (in the prius case) ... most modern engine adjust, but ONLY lower (avoid knocking) but not higher ... so it is no benefit to use a more compressible fuel. Just my two cents ... (oil companies must like you )

 

There was an interesting show on CBC's Market Place on this subject. It's a long neglected con game: when you roll into a typical gas station there are myriad grades available, and not-so-subtle hints that each up-step in octane is "superior" in some way.

OTOH, the percentage of vehicles where the manufacturer recommends higher octane fuel, typically due to higher compression engines, is negligible.

 

In theory, they could, but the present Prius valve mechanism just doesn't have the needed adjustment range. This is where electric valve actuators could shine, if they ever reach the market. Completely abolish the camshafts and timing chain, and get a full range of valve adjustments and cylinder deactivation options in one fell swoop.

 

Our previous Civic Hybrid had dual cams lobes with different lift range. Normally the car used low-lift cam lobes, but under heavy load hydraulics shift over to the high-lift lobes. Climbing one overpass every morning, you could feel the kick-in-the-pants when it shifted.

 

In other words, valve timing controlled by software. That will happen as soon as somebody develops electric actuation that matches the reliability, cost, and energy consumption of mechanical actuation.