Interestingly enough the July Car and Driver just came out and they have an article on this exact topic. Just came out so I can't find a link just yet.

They tested four cars - Honda CR-V, BMW M5, Ford F-150, Dodge Charger. The Honda only recommends 87 so premium did nothing - no surprise there. With the other three where the recommended octane is 93, dropping to 87 (91 on the M5) basically reduced hp. The M5 got better mpg with 91 (by .7 mpg), the Ford and Dodge got slightly better with 93 (.6 and .3 mpg respectively). The 0-60 times were all quicker with 93, as were the quarter mile times. Makes sense that would follow with the hp difference.

So their bottom line answer to the question "does premium matter", they concluded "it depends".

They did offer a note on knocking that I found helpful. They did say that consistent knocking will damage the engine over the long term. However periodic knocking will not. Once these engines detect knocking, they back down immediately. So modern engines running on 87 should not have any long term issues because the engine isn't actually knocking. The cars detect and adjust immediately. They ended with this quote from Stephen Russ, senior technical leader for gas engines at Ford, "[knocking] is usually detected and addressed within one or two combustion cycles and poses no threat to the engine."

It would seem the only end result is there is less hp available. And since a hybrid is supplemented by the electric engine anyway, I can see why the 450h might have zero "butt feel" difference in performance. Mpg difference could easily "depend" based on how and where we drive. Might explain why many of us get different results.

 

I think this is a great, accurate hypothesis. I noticed some local Alon gas has gone down one octane number from 87/89/91 to 86/88/90. I’m not sure why the octane was decreased, as our elevation obviously hasn’t changed...

 

Somewhat similar to my hypothesis. My tip is if gas is high get the regular. If gas is cheap like how it is now, get premium. But if it makes you sleep better at night get premium. At the end of the day it's your car and your personal preference.

 

Agree. I used to be pretty adamant about using premium, but that was largely driven by my misunderstanding of knocking and how these engines deal with it. I thought that being in a state that prevents knocking might have some long term effect, but now I understand it does not. Long term knocking does have an impact, but these engines won't allow that. They simply adjust the timing and move on. The article covered the fact that cars don't know what fuel you put in - the engine runs, detects what's going on automatically and adjust accordingly. Also makes a lot of sense because in spite of the octane rating listed I bet there is variation. 93 might be 92. So engines have to account for this unknown and still operate.

So I kind-of agree now that folks should go with the fuel they like for their own personal reasons.

 

If you get bored reading this thread, you can go to the hybrid section and read about the same worries. I use regular from Costco, when in town and the lowest grade on road trips. I have been doing this for 30 years of road trips and never had an issue. 2018 450HL

 

I'll offer the same opinion I did in the hybrid thread.

Bottom line is it does not matter but your results may vary.

Several months ago Car and Driver did a test with four vehicles and ran dyno and acceleration tests using regular and premium, all in vehicles recommending premium. In all cases, hp dropped using regular, but not so much that it would be noticeable to the driver. IIRC like 4-8 hp. MPG impact varied - three got worse, one got better. But by tiny fractions - tenths, < 1 mpg. They concluded that in real world conditions, neither of these things would likely be noticed by the driver.

They also made the point that modern engines are built to react to octane levels within a couple cycles. The only thing that causes engine damage is persistent knocking, these engines won't knock very long, if at all. Basically safe. They adjust immediately.

So the moral of that story was use what works for you, and understand that your results may differ from others depending on how and where you drive. In my 450h, I notice a consistent 1 - 1.5 mpg drop using regular. But drives exactly the same.

 

I have a late year 2016 RX 450h. I started out using regular gas for several months before switching to premium for 2 months (to determine if premium gas was worth the extra cost). I saw no difference at all in performance or gas mileage, so I switched back to regular. After 3 years and 4 months, my RX still performs like it did when I first bought it. I see absolutely no justification for paying up to 40 cents a gallon more for premium gasoline. Perhaps it might make a difference in cold weather or high altitude locations but, here on the central coast of California, it definitely doesn't.

 

I have pretty much achieved the exact same results as you. In some tanks, I see a little better mpg with regular 87 vs. 91 octane (highest available in my area). I also had a dealer read the knock registry & nothing was logged.

 

I was drawn to Lexus for replacement of my 2008 Highlander Limited because I wanted a more luxurious vehicle which would get somewhat better gas mileage and help the environment at the same time. So I have been exploring the RX 450h (or RX 450hl). In fact, my wife has a 2020 Toyota RAV4 Limited Hybrid that she is happy with (40+ mpg), albeit the number of recalls that the car has had.

However, I’m very confused about the actual fuel savings between the RX 350 and RX 450h. Because the RX 450 requires premium gasoline, it would cost somewhat more at the pump.

Assuming that I drive a RX 450 15,000 miles per year, at an average of 30 mpg, and at $2.97 per gallon (for 93 octane at Exxon), the fuel cost would be $1,485. But for the same distance on the RX 350, which can run on 87 octane ($2.19 per gallon), at an average of 23 mpg, the annual cost would actually be lower, at $1,428.

I thought I was missing something. So I asked the dealer and the response was: 1. You can try 87 octane in the hybrid and see if you lose MPG after getting a baseline from a few tanks of premium. 2. Look at the other 3 benefits of the hybrid (less pollution, quieter, front brakes last longer). If in the end your math doesn’t make sense for the hybrid, please take advantage of an RX350 that uses 87 octane.

Thoughts, anyone? Please don't flame me if I appear to committing sacrilege.

 

No one should flame you, as you are doing a great job with your homework! I have a 450h & I get better mpg with Top Tier regular vs non-Top Tier premium fuel. Top Tier premium is about the same as Top Tier regular. I seriously doubt if you will regularly get 30 mpg, unless you do a lot of stop & go driving. I’m averaging 26 mpg highway on my 450h. On really windy days, you will see around 22 mpg highway. The rest of the tree hugging stuff is just a personal choice. Sure, the brakes last longer, but they don’t stop quiet as good. What you benefit from in the 450h over the 350 is quiet. When running on battery (below 40 mph) it’s a super hushed ride. The 450h also does not seem to suffer from the horrid exhaust/transmission droning that is driving customers away. Drive both & then decide - keep up the great work on your research, as the extra cost of the hybrid does not equal savings, it gives you a different ownership & driving experience. I hope that helps.

 

There are many threads here about wjhether you need premium gas. You will find that there are many people who do not use the higher grade, and I am one of them. I addition there are many threads on savings that are not related to MPG and the fact that hybrids do save money over non hybrids. MPG savings are just nickles and dimes and the real savings are in the other maintenance items. Enjoy the reading.

 

Depends where you do your driving. I live in Los Angeles and my drive is usually on the 405 freeway in traffic. I have a 3RXh and I usually put Arco 89. I easily average 31mpgs. If I did the same commute in a non hybrid suv I'll probably be lucky to get 17mpg. YMMV.

 

Just curious; what mileage are you getting with your Highlander? Forget EPA numbers; the RX350 should get pretty close numbers to your current Highlander unless you do a lot of highway cruising. The rated 23 mpg combined is very optimistic for the 350; while 30 mpg is quite achievable for the 450h (especially if you're used to driving a hybrid like the RAV4).

I used to have the '16 RX350 - I was lucky to get the equivalent of 18 mpg on my usual commute. My previous vehicles were all sedans (and manuals), so they were closer to 23 mpg for comparison. Got tired of having to fill up every 5-6 days (this was well before Covid), so traded it in for the '18 RX450h. Never regretted it one bit. I'm still getting well north of 30 mpg; plus all the other benefits of the Hybrid over the regular RX.

As for the type of gas to use - it all depends on how sensitive you are to the driving 'feel'. Lots of people don't notice a difference. For myself, I can feel the difference in between brands of gas at the same octane, let alone different octanes; so I stick with Shell 91, which has given me the smoothest driving experience (and best mileage).

 

Thank you for your input. But my point is that the savings in hybrid fuel economy would be offset by using premium fuel to achieve the desired performance. BTW, my Highlander gets a lousy 17 mpg city and 25 highway, which is why I'm so interested in the RX hybrid.

 

So you're able to use 89 octane to achieve this performance even though minimum recommended octane is 91? As an aside, I can't even find 91 octane at any of the branded gas stations in my area.