WE have massive price swings through a fortnight cycle, price goes up and down around 30 cents per litre (USD$1.00 per gallon), currently around the middle which is AUD$1.60 per litre for 95 OCT. So at that rate I fill up 60 litres (70 litre tank) is AUD$96.00 - $USD67. The price recently was AUD$1.80 per litre.

 

This is the same story! Lexus DOES NOT recommend 87 it says you MAY use 87.
It's kind of a warning not to go below that level of octane as the computer may not compensate, no such warning for going higher.
I agree with you and I use 91 or 94.
Someone here contacted Lexus and was told that their tests were done with premium gas, don't know if 91 0r 94 octane, though.

 

This is a quote from hemmings.com ---- https://www.hemmings.com/blog/2014/0...-priced-fuels/ ---- which generally concludes that higher octane is not needed unless specified by the car manufacturer. "On modern computer-controlled cars with fuel injection, the computer is constantly monitoring fuel trim and detonation and making appropriate adjustments in the timing and fuel air mixture to compensate for engine knock"

The key question is does the change in engine timing from using higher octane fuel cause the transmission computer to behave differently?

 

That's a very good question! These days with electronic interconnections it probably does, this is an empirical observation on my part.
I just recently discovered that the HVAC takes into consideration, not only the setting, but also if you have the seats heat on and regulates the amount of heat & for how long it will be on. It makes the ambient really comfortable, but there is something in me that longs for the control to be returned to...me!

 

With the various computers transferring data on the CAN Bus throughout the system, I would agree that the transmission computer might just change the shifting pattern. I will test my empirical capabilities and put a few tanks of high octane through the vehicle. Thanks Cocal.

 

Great RXTimes, let us know what you observe.

 

https://lexus2.custhelp.com/app/answ...xus-vehicle%3F

RecommendedMinimumOctane Rating: 87 350/91 450h

 

Yep, and the official US Dept. of Energy Fuel Economy Tests are done with Regular gas for the RX 350 and Premium Gas for the RX 450h

https://www.fueleconomy.gov/feg/Powe...RX&srchtyp=ymm

 

There is confusion; in that doc that you provide the link for it does say recommended, but this is what's in my owner's manual:

Select octane rating 87 (Research Octane Number 91) or higher. Use of unleaded gasoline with an octane rating lower than 87 may result in engine knocking. Persistent knocking can lead to engine damage.



This is NOT a recommendation, but a warning not to go below 87. I imagine that if one goes below 87 the computer could not compensate.



So here we have two documents saying the same thing, but with different meanings. In the end one does what one think it's best.

 

In agreement. The computer is designed to run from 87+ in the 350, so unless you put in diesel (happens to the best of us) or live in a high alt climate (I have heard Denver gets 85 seasonally?) no really way to go wrong with any tier of gasoline widely available.

Now the bigger question is most engineers on interviews have written about power numbers, and octane the vehicle was designed for; vehicles performance is best suited with the octane number the engineers designed the motor to run with, and you are wasting money by pumping in more expensive or cheaper gas. With Lexus stating anything 87 and above, which did they use? Its cut and dry for other vehicles like the GX or even LX where they specify a single octane (the motors are used in other vehicles where they are spec`d for lower octane and have different power numbers). The same motor in the RX is used elsewhere where 87 is the go to.

 

Great question !!! I did not do this, but a forum poster, quite a few months ago, said that he did contact Lexus and they told him that all tests were done with 91 octane. I believe that was from Lexus Canada, am not certain.
I can't remember his name nor the date or subject heading alas. I tend to believe this as in every other country the recommended octane is 91 minimum.

 

Over the years, there have been many posters on here that claimed to have called car manufacturers, tire companies etc, and have gotten conflicting answers. I believe they didn't reach the right people and are just given any answer they think you want to hear. JMHO.

 

The only reason why I do give credence to that poster is that elsewhere in the world they use 91. Here in North America they dumb-down all maintenance to a non optimal level, that applies to all makes.

 

https://www.economist.com/babbage/20...-needs-premium

 

I bought a new 2018 RX-350 F-Sport to replace my 2015 after it was wrecked. I reported the "hesitation" issue to the service manager at my dealer when I took it in for the 10K miles maintenance. He said (with NO hesitation), "new transmission". I believe it, because I have been mixing 87 and 93 octane gas for awhile and raising the octane that way makes absolutely zero difference. I always drive it in sport mode, but that also makes little or no difference.