naytrix

The manual says: "87 or better". So that provokes a number of thoughts:

1. Fueling with 87 seems like the car isn't running to it's potential power and gas economy wise.
2. Putting 89 in seems silly since it's seemingly just a mix of 87 and 91.
3. Is putting 91 into a car that allows 87 wise for long term longevity?

My main concern is that I want to pick a grade and stick to it, but I am having doubts about using 91 all the way mainly because I don't know what the actual difference is between cars that were tuned to use 87 or 91. For instance, if a car that expects 91 but gets 87, the engine starts clicking in a while. Are there disadvantages or advantages of using a higher grade besides higher cost and slightly better mileage and power?

What do you guys use?

Joeb427

iTrader: (1)

For years this same engine called for premium in Lexus models and 87 in Toyota models.
I compromise and go 89 but always tempted to go 93 in our '15 for optimum performance.
Heck,with the 5K-6K per,I'll probably go 93 now.

Oldfart

It is same gas, with same amount of energy and burns exactly the same. What is the point of using higher grade gas in engine that is tuned for lower grade?

Let me say it again if engine is not tuned for premium gas there is no benefit using it.

Joeb427

iTrader: (1)

I don't believe the 3.5L in the RX was tuned for 87..
Same engine since '06.
Toyota called for 87 and Lexus premium.

Premium gave you 4 more HP and a bit more torque.

I feel the same way about Toyota's going from 5w30 to 0w20 to gain a few tenths more MPG average for the rising CAFE requirements.Though I still will use 0w20.

Gas is cheaper now and I don't do a lot of miles per so I don't mind using a higher octane than 87.

Oldfart

I am sure you understand that cheaper gas and a fact that you do not mind using higher grade doesn't change compression ratio and timing values that are programmed into computer.

Just because it is called "premium" or has a higher number doesn't mean that it burns any different once it is ignited .It is same gas with an extra additive to make sure it will not ignite sooner than it is supposed to.

Our engines constantly adjust timing, even at idle timing jumps all over. Computer is using pre-programmed timing tables for various conditions. It is quite possible that Lexus engineers programed timing tables assuming that people will use lower grade gasoline. Since engine doesn't know that you have filled up with premium grade gas it still will use pre-programmed timing table and ignite gas based on table value. So it is very easy to tune engine for a lower grade gasoline all they had to do is change timing values.

naytrix

@oldfart: then how would you explain that onboard computer reports higher fuel economy with Premium and noticible performance improvement?

JDR76

I tried a few tanks of premium in my '13 RX and could not notice any difference in either power/performance or fuel mileage, so I continue to use 87.

naytrix

I made the same trip on 87 and 91 and the average fuel consumption as reported by the car ("since refueling") was 21mpg and 23mpg respectively. Also I did notice an increase in performance, but I could concede that it might be subjective...

Oldfart

naytrix,

When someone says "trip" I am assuming freeway driving. On a freeway engine works in a relatively comfortable zone 99% of the time and that is not when higher octane is needed. Higher octane needed under stress at high RPMs usually above 5K or at very low RPMs when car just begins moving. Both of these conditions mostly non existent during freeway driving.

Difference in reported MPG could be contributed to different wind direction or elevation levels which are unnoticeable for human eye.

I used to own 2005 RX330 which requires regular gas so just to cure my own interest I'd fill up with premium gas for 4 consecutive fill ups and for my commute my reported MPG remained same and like you I swear it felt like car had extra peppiness to it. Whether it really did or was it just a placebo effect I do no know but my MPG remained same.
My Acura calls for premium and I've done similar experiment for 4 consecutive fill ups I'd fill up with regular gas but my MPG also renamed unchanged. I also used live scanner just to see if timing being pulled from map and I had to go out of my normal habits in order to do it. For example driving at 40 MPH I'd manually shift to 5th gear and hold it in 5th I'd try to floor it only then I'd see timing being pulled. Normally computer just shifts to a lower gear to reduce stress.

Other things to consider is outside temperature and level of humidity, since for most internal combustion engine fuel to air ratio is 14:1 I'd think that 14 parts of hot dry air will play a bigger role than slight difference in octane rating.

By the way I am usually much smarter after my second glass of wine so I will try to read what I just posted and see if I need to add anything else when I reach my smarter condition.

justin1203

If you can't afford the premium gas price, don't purchase a premium vehicle.

I drive about 15k a year, probably higher than most. It's 30 cents more for premium 92/93 over regular 87. Doing the math, it's another $225 a year. To argue over this, is silly.

Oldfart

Justin, would you like to contribute to a topic? First of all15K is not higher than most, it is national average.

Question to you Is $225 you spend extra per year benefit your car? you or your family? or mostly oil executives?

steveo55

I use 91 on both cars. Thats what my IS350 says to use so I figure might as well do the same on the wifes RX that way my hands are trained to always reach for the 91 octane so I wont ever accidently use lower octane on my car

hovbuild

In the end after 10 years of saving 250+ using regular and not really noticing a difference in mileage or performance, do you think you'd get less for the car if you told the buyer you used regular?

Oldfart

When I was selling my 2005 RX I wrote that car doesn't require premium. If Lexus can do that so can I.

lexus114

i tried 92 octane fuel in my 15 and the fuel millage was horrible! 16mpg. and lost power