I agree there is an "artificial intelligence" or "machine learning" function in the ECU, such that it takes a bit of time to adjust to the driving regime. I don't know how long the feedback loop is -- maybe a couple of tanks of gas, anyway. If a driver will use the odometer, the actual amount of gas used, and a calculator, there should be no placebo effect involved.

 

By empty I didn't mean for anyone to take me literally. Just down to about 3 gallons when the low fuel warning light turns on is enough to avoid dilution effects.

 

I've kept close track of mileage by hand for the last 3,300 miles using 87 octane. (All the fuel was purchased from Top Tier brands, but only one of the 12 fill-ups was from a station displaying the Top Tier logo.) My intent is to now do the same thing with 93 octane, if I can get my cheap self to spend the extra money. Where I live 93 is $.50-$.60 more per gallon than 87.

I'll report the results of my mileage test on this thread when complete. The average mileage with 87 octane has been 22.9 mpg in mixed driving. "Performance" is much more subjective and I don't know that my driving style will elicit any difference, but I'll try to pay attention.

 

Only 91 from top brands. Just for peace of mind.

 

Only 91 from the best brands including Costco.

 

Use 87 from Top Teir when possible as they are typically the same price. Haven't experienced with higher octanes.

 

we're finishing up the current tank of 87 and will switch to 91 going forward. the RX was filled up by the dealer with 87 when bought brand new a month ago, we decided to stick with 87 during our week long road trip to nocal, but now decide to change to 91 for good just for peace of mind as others said.

 

FWIW I've used at least 91 octane since new and have not experienced the acceleration/hesitation problems, that others have, to the same extent, I do occasionally feel the hesitation, but I think it's the transmission hunting for the right gear, a programming problem.

 

Cocal, what brand of gas do you use? I've been using "Top Tier" Shell regular grade with no hesitation at all. 91 octane is reaching close to $4 a gallon here!

 

Here I use 90% of the time Petro-Canada and 10% (approx) Shell.

 

New member here, old guy age 68 who's been buying gas for a long time. We have 2 new Lexus cars, I have 4 antique muscle show cars, former drag racer many years ago. I just traded my 2018 XSE V6 (301 HP) Camry for a new F -RX 350. I run only Top Tier 87 gas, that's what I ran in my Camry...and it ran great! I'm very hard on the throttle sometimes. That's what I'm running in my new RX, too. My opinion is you are wasting your $ for nothing. I do believe you would get a tweak more performance and mileage from hi-test. But not enough to make a difference to justify the cost. But...hey...it's your money.

 

There many ways to calculate waste, if you're only going by MPG I'm with you, but when you take into consideration how much cleaner your valves and the internal parts are, free of combustion deposit which are greater in reg Gas and therefore you'll have less mechanical problems and neither the engine nor the injectors will need to be cleaned then it makes sense. But you if you want to save now and pay later that is up to you. I've got 10 yrs on you and also an x rally driver.

 

Well, if you were a racer then I'm sure you're familiar with spark plugs, their specific heat ranges, gaps, etc. If you run a higher octane gas, then the plug will burn hotter, the longevity of the plug will be shorter. That means the plugs will have to be changed sooner ($$$), and the temperature of the cylinder(s) and engine will be hotter. Surely you would agree with that, right? So...it's a trade off either way. Honestly, I don't see myself with this car in 5 years time. It's totally paid for, so it's not a $ issue for me at all. And...then there's the warranty, too. It's the electronics I worry about, Just as a point of info for people, I will say this... My 2018 V6 (same engine as the RX) Camry was really quick. I never used the paddle shifters even once. I tried it on ECO, and did not get any return at all for mileage. I tried it on performance, and I wasn't impressed. I just kept it in normal, ran 87 Top Tier and it was GREAT! There is one thing...these newer transmissions take time to learn your habits. It took a long time for that car to learn. I would come off a ramp and jump on the car and it would just die, it was scary. The same with passing when you really needed to pass fast on a back road. Then it just went away in time and acceleration and shifting were instantaneous. The RX has a smarter trans, but there is still learning process for the computer. Your RX will have more pop in time. I'm talking over 1k miles, or maybe a couple K miles. For those of you that have those type of symptoms, your RX's performance will get better. I only have like 500 miles on mine now, but I had a 2021 loaner we put like 1200 miles on and it had more pep. Everybody should run whatever works for them. My point is, a higher octane gas will not make your RX a race car, nor will the shifter paddles. Second, the car has to break in before it reaches it's potential. Rather than take a brand new car and experiment with so many variables, I think waiting 5K or so to get a good baseline on MPG, etc. may be a good idea.

 

For me it is all about max performance. I do not care if the mpg is the same or not. I am sure those specs about the car you see on the manual were pulled using a higher octane gas than 87. I mentioned I also have a MDX 2020. That car at least is more transparent about the gas requirements. It explicitly says 87 is a minimum and 91 is recommended. Even mentions reduce performance. Not sure why Lexus decided to skip that part on their manuals.

 

I understand that the first couple of RX generations were premium-only gas, and it was considered to be a drag on sales. When Gen 3 came out, the sales guys were all thrilled to tout the "regular gas" feature, as I heard when looking at the 2014s and 2015s. So I believe it's all marketing driven, including the "minimum required octane" lingo in the manual.