JerseyJim

I concur with erom43. I just took a 200 mi trip over the weekend averaging about 68 MPH on the interstate and got 23.1 MPG after refueling on a '15 RX 350 AWD. Average temperature was about 40 deg. F.

Non

It's important to remember that driving style affects the MPG a lot. Jack rabbit drivers get poor gas mileage.

Jared96

Thanks everyone for the reply’s. I’m running anywhere between 32psi (factory sticker recommended) and up to 38psi to see an improvement to no avail so I’m back down to 32psi. The tires are Michelin all seasons. On these panhandle Texas highways, they’re flat, straight and very low traffic. With the cruise control set at 75 on these highways, we can rule out my in town driving habits. I think just for ******* and grins, I’ll pull one of the front spark plugs and look at the condition of it. The car has 154k miles on it now, so I’m sure they are due to be changed. However, there are no other drivability issues. So hopefully, with new plugs she’ll see an improvement. I’ll keep you all updated.

cory143

Have been averaging around 18.5 since I bought it 3 months ago and 4,000 miles ago. 2010 RX350 from 101K to 105K. I'm taking my first 400+ mile highway trip this weekend. Let's see how it goes.

davrober

Im down to about 16.5 average. It says to use high test and thats aggreevating because my son bought a 2013 same as mine and only needs regular. Thats 60 cents a gallon less here. My 2011 now has 95000 miles on the ODO Meter so its probably ready for coils plugs and wires so we'll see if it gets any better.Id love to get new GMC but gosh darn theres really nothing that ever breaks on the Lexus or Toyota nd my firends GMS denali is always in for service for something or another. Might go electric with a rx350xl if they make one.

RichS

I've used regular for at least 5 years. From everything I've read/been told, it's the exact same engine setup. Lexus just decided to lower the official octane requirement and took the hit on reported hp/torque - from 275/257 to 270/248. Unless you're using the extra 5hp for drag racing or something, go with regular.

The maintenance schedule calls for plugs etc at 105K, but our dealer said they don't bother. At 185K, I finally suggested it was probably time to change them, and they agreed. It's not an easy/cheap job. I noticed no difference inn driveabiliity or mileage after the work was done. If you're at 16.5 on the highway maybe it's worth a try. I get 17-ish in city driving, but still 22-24 on the highway.

Clutchless

Every modern vehicle has knock sensors, also known as anti-detonation systems to allow for timing adjustment for octane variations. My 1994 Mazda MX-6 had knock sensors 25 years ago.
Toyota only specified high test for the RX (and ES) so it could have bragging rights that the engine was more powerful than the one in the Highlander or Camry.
You can hardly tell the difference in acceleration running regular over high test gas even if you are a very aggressive driver.

davrober

I just had the 95000 mile service. I asked the dealer if I had to use 91 octane on my 2011 rx350, and he said no you can use regular. I said I thought the manual said 91 and he said read it again . It says for better performance use 91 but the car runs fine on 87. I said what's the difference between my 2011 and my sons 2013 engine and he said there is no difference after 2016 the compression is higher and there are changes but even those where ok on 87. I said where do I get back my 4000 dollars I spend in 8 years on 91 , he laughed and said send the bill to Toyota let me know how it turns out. Good thing hes a friend of mine lol.I should have asked him a few years ago.

davrober

I just had my 95000 mile service and said change the plugs. The service writer said Ive got another 10k left and probably could go a little more but I said do it. Normally Id have just done it but with my arthritis its tough working on the car any mores I bit the bullet and said go ahead. . So far so good. Runs good on regular and at I had 17 mpg last top off which was a bit better but Ill have to see a few more to see if its changed. By the way having them change plugs is a bit costly but I cant do it anymore so Im stuck but its good for another 95 k so over 8 years its cheap.

Non

There's nothing wrong with letting the mechanics make some money, when you can't or just don't want to do the work yourself. They need to feed their families too.
You should continue to investigate your poor gas mileage, 17 MPG is not OK.
Did you ever clean the Mass Air Flow (MAF) sensor? Maybe try doing that, a can of cleaner costs less than $10
How are you measuring it? Do you divide miles driven from last fill-up by the gallons you just put in the tank? Or do you just read the car's display?

davrober

Im using the display , no haven't cleaned the MAS but spraying it and cleaning it can cause it to malfunction and they aren't cheap , at least that's the way it was on my BMW 3 series.
Im hoping its not the module that controls the fuel air mix .

RX in NC

Cleaning the MAF sensor properly will not harm it. You just have to do it correctly (with the proper MAF sensor spray cleaner) and NEVER touch the elements inside the sensor once you have removed it for cleaning.

davrober

My 2011 rx 350 and is getting 16.5mpg on 91 octane. Been using it since new. Dealer said regular was fine but performance might be a little less. Used 87 octane now getting 15.4 mpg . The point is out here on Long Island gas is $248 /gal regular and $3.05-3.08 /gal for 91 . for a typical 10 gallons that's $24.80 for reg and $30.50-$30.80 for high test. Even though I get lower mpg for regular , its still a lot cheaper . for that extra 10 miles it costs me 60 cents a mile . for the entire fill up with regular at 150 miles its .163 cents per mile and 91 octane is 18.5 cents per mile . Over a year at 11000 miles per year that's about $220 dollars less using regular and I really don't see any acceleration differences. Now over the life of the car which is 8 years almost to the day that $1720 more for gas . I like seeing 16.7 mpg on the fuel readout around town better than 15.5 but when it rings up each week I really like seeing under $25 for a full tank and not $30+. Just my two cents . I actually had them change the plugs at 95000 miles just because and I really don't think it made a difference but I come from a world where we used to change then every 12000 back in the day of muscle cars when I grew up.

Non

It's fun to calculate stuff, isn't it?

Yes, 15/16 MPG for city driving is probably all we can get, but try different brands of gas and also try other gas stations. I notice about 1or 2 MPG difference between gas stations. Recently, my local BP has ben the best for me.

snowman22

I would not complain about 15.4 mpg. I’m assuming that’s city driving. The average on that car is city driving 12-13mpg. That’s cold weather. 14-15 summer. Continue to use regular. The car computer will adjust for the difference in octane. I know— been there with a 2011 RX. Sorry to say I simply wasn’t going to keep that car with such poor mpg. Nice car all around except for that mpg. Have had two RXH hybrids since. Great cars excellent mpg. Current 2019 hybrid is 29.4 summer 24-25 right now. Mpg. Love this car. That’s on REGULAR.