For those of you who live in a state with Kroger grocery stores, you can earn some nice discounts on their gas by shopping there. I usually get between 70 cents to a dollar a gallon off every fill-up. That makes it a lot easier to use premium. Kroger usually buys their top-tier gas from Shell. They use annual contracts, and I've never seen Ethanol included.

 

In Pittsburgh we have Giant Eagle Supermarkets coupled with their GetGo mini-marts and gas points. Yeah, if you shop there anyway it's free gas money. But it doesn't change the equation of whether it's worth it to spend 20% more for premium. I don't think it is. Some here do. But whether you pay with grocery points or with cash the fact that you use the points doesn't make it cheaper. It's an illusion.

 

Er... it is a 2.4 liter. Typo?

 

Nope, the RX350h has a 2.5L Atkinson cycle inline 4.

 

I found this:

"A by-product of this is that Atkinson cycle engines actually run best on lower-octane fuels. The slower flame propagation of high-octane fuel is detrimental to such an engine, and Prius owners who have made the mistake of running premium fuel in their cars have been rewarded with misfires, check engine and hybrid system warning indicators"

I also found comments stating that the Atkinson cycle, with fast propagation fuel (lower octane) are ideal for hybrids because the engine restarts faster, making for smoother transitions between gas and electric.

YMMV

 

Now that is important information. Where did you find this?

 

Everyone needs to use the grade of gas that they are comfortable with.

 

I know this is a great debate topic but has anyone actually tried running on 91 versus 87 and noticed any measurable difference in MPG? I plan to run it on 87 if there is only a 1-2 mpg hit on the efficiency. I have 400 miles on the odometer and am still on the original tank the dealer provided which I understand to be 87 based on what I read here. At this time I'm not quite hitting the 37 mpg city mark yet but its a new engine that needs to be broken in I presume. Thanks in advance, this will help me avoid having to do my own experiment.

 

I have never tried 91, only 87 and I'm averaging over 40 MPG so there is no need to bother with the 91 esp with the 15-20% additional cost on 91.

 

I believe using 87 octane would decrease your horsepower by maybe 1 or 2.

Used to be that the cost difference was not that great between octane, today there is.

 

Thank you @jahnjva and @ggebhardt, exactly what I wanted to hear. its about a 40 cent difference where I live between 87 and 91.

 

Have owned my RX350h for about 3,500 miles so far. The first 2,000 or so I used 91-93 octane exclusively. Averaged 35mpg highway and 37mpg city. Switched to 87 and have noticed no difference whatsoever in gas mileage or performance. This is not a performance engine and the Atkinson cycle probably numbs any possible difference in performance if any. No complaints on 87 so I will keep it there and save a few more $$$ than this amazing car does for me already.

 

I'm relatively new to the forum (first Lexus) but are there any Toyota/Lexus techs here who can definitively state that running 87 doesn't do long term harm to the engine? This engine is the same engine (A25A-FXS) as the ES300H and that car states clearly that 87 is the fuel to run. Granted the HP output (~220 vs ~240) is different which means there is at minimum some software differences. If so, my hope is the computer runs a different tune to reduce power and safely/reliably run 87.

 

I doubt that any Lexus tech is going to issue a “definite” proclamation like that. What is definite is page 570 of the manual, that definitely states that the minimum acceptable octane is 87 for the RX350h but is 91
for the RX500h and the non-hybrid RX350 turbo. I’d say it’s pretty definite that if the RX350h would be subject to damage on 87 octane gas, Lexus wouldn’t allow it as they do right here:

 

Its shocking this is in the manual, to me this is ambiguous. I'm a little upset that they say "you can run either fuel" as It leaves a lot of room for people to interpret it their own way.
Anyway will run 87 and cross my fingers the computer runs a similar tune as the ES300H.