I myself would not spend the extra money on premium fuel for a RX. My Mustang is tuned for 91 octane.

 

Mistyped, I didn't have a gen 1, only gen 2, 3 and now 4. So yes, Gen 2 required premium as did Gen 3 to 2013.

 

This comes up a lot.

The short version is your car can run on regular. Most data on the topic will point to the fact that you may experience a tiny drop in hp and a tiny drop in MPG IF your car recommends 91 and you use less. Whether you do or not depends on a lot of other factors - where you drive, how you drive, etc. The differences might not even be noticeable. Best advice I can give is try 2-3 tanks on one, then 2-3 tanks on the other when you are able to keep the driving conditions fairly similar and just see for yourself what you like and go with that.

I've done that and I do notice a difference with premium in my 450h, so I go with that (and as previously mentioned, in my manual 91 is recommended, but 87 is the minimum). Others who can't tell a difference or drive enough where the cost matters use regular.

 

You know the best way to go with this is to try for yourself. After a couple of fills with premium see what it's like than go back to regular after a couple of fills and see how the driveability is affected. These RX's have some quirks in their software mapping for the transmission, some people are perfectly happy with them while others seem to have numerous issues with how the car drives. Being the latest model maybe Lexus are using updated software, I don't know, but a couple of tanks of premium won't cost too much and certainly won't hurt the engine at all.

 

Which ever grade you chose, remember to use a “Top Tier” fuel.

 

Awesome! After reading this thread I had to move to the middle octane just to be on the safe side. Killin me Smalls, killing me! lol

 

rxtimes2 is right, use "top tier" gas and you should not have any problems.

 

Does anyone else find it odd the 2021 manual says "use 87 or higher"? Using a higher octane fuel than the engine is designed for doesn't do anything. It's a complete waste. Either the engine was designed to prefer higher or it doesn't. I realize modern engines basically detect what's being used and adjust accordingly, but a car's MPG and HP ratings would be based assuming some kind of fuel. If the ratings were based on premium, they would recommend premium. If they were based on regular, then using higher octane fuel does nothing for you.

Saying "or higher" seems strange to me. I want to know what the engine was designed for and what fuel is assumed when calculating published MPG and HP ratings. Fine if I can use less, but being so vague seems odd.

 

As mentioned on this tread 1 or 2 years ago, it was designed on 91 octane (per Lexus Canada)
Lexus also knows the reticence of northamerican buyers to use premium so that's why there is that writing, the computer can only compensate so much.
This is also a question of price vs cost as by using premium one gets other benefits which will result in lower maintenance cost, but if only keeping the vehicle for 2-3 years there would be be no ROI so that's moot.

 

The '87 or higher' reference isn't odd or vague to me. The manual is written so owners know how to prevent damage, not obtain optimal performance (whatever that means.) Preventing engine damaged is accomplished by using 87 octane or higher fuel, per the manual. It's not much different than 15A residential electrical circuits being required to use 14 gauge wire or heavier. There's no harm in using 12 gauge and one may chose do so for a number of reasons. Choosing 16 or 18 gauge, though, could result in a fire.

 

Me neither. Those crafty engineers have used VVT, dual port fuel injection, and electronic ignition all together to get this engine to burn the 87 octane with no spark knock, probably demanded by the marketing department. I'll bet their reported mpg, hp, and torque figures are achieved using considerably higher octane fuel.

 

This is why I found it puzzling.

If their published stats are based on higher octane, I would expect the manual to say what mine does (2016 450h).

But to just say "Use 87 or higher" begs the question if higher than 87 is required to achieve "optimum engine performance". I suspect it is. To be silent on the matter is unusual. Because if you can get optimum out of 87 there is no need to say "or higher". Saying "or higher" implies that can and would take advantage of a higher octane.

It's just weird they talk around it. Seems to me they let the marketing department spend a bit too much time with the manual....

 

I agree -- engineers would not weasel-word it that way. The giveaway was the first words out of the salesman's mouth when I expressed my admiration of the 2015 sitting in the showroom. ".... And it runs on regular gas!"

 

That's what the Owner's Manual is, a compromise between the Engineering Dept and the Marketing Dept.
If you want to know what the engineers wanted, look under "Severe Service Schedule"

 

IMHO the "or higher" is for those that think middle or premium may hurt their engines, just in case their local gas station is out of regular. YMMV :-)