Like lots of other people here, I only put regular in my wife's RX300. Not only that, but I now only put regular in my GS400. I notice no difference in performance with the sweet V8, but of course I rarely push it more then 80%. Unless you have forced induction, I say save the cash.

 

I've discussed this on another forum so lemme see if I can clarify something. (I have a 2004 RX330)

The higher octane 91 ON THE RX ENGINE *can* make it smoother and reduce tranny hesitation. Here's why:

The compression ratio of the RX engine is like 10.4 or something, which is about requireing 91 octane to avoid detonation. However, the car's computer (ECU) can use a trick: retarding the ignition timing and downshifting to reduce detonation (knocking). This technique is effective enough that the RX's ECI can allow 87 octane gas to be used. The drawback is, with retarded timing, you get less power efficiency out of your gas. This is made up for (approximately) by downshifting, but as most 87 octane RX users experience, this means a rougher acceleration as the car double downshifts. (Annoying). In addition, the higher RPM's increase wear on the piston rings and journal bearings. There's always a tradeoff.

If you are 99% light on the acceleration, then 87 is probably better for you. It's economical, and since you don't demand hard acceleration, the car won't need to double downshift that often.

I only recently read about this, so I had been using 87 for the first 1.5 years of RX ownership. I recently switched to 91 (and feeling raped by gas prices) to see the difference. I must not have pulled the right fuse (or not long enough) because it still took awhile for the hesitation to reduce as the ECU adjusted the parameters.

My conclusion:
- 87 is just fine and even better if you are soft on the acceleration
- if you like to push the pedal, then you should move to 91 as that is what the engine was designed for. With 91, it will operate most efficiently (better power for acceleration)
- 91 won't affect MPG much (as I've experienced) unless you are doing a lot of stop and go city driving. Freeway driving will totally overshadow the 91 efficiency increase.
- medium octane, or 89 is the petrol industries joke, sorta. No car manufacturer is designing engines for 89. It's either 87, or 91 (for the USA, that is). If you're knocking at 87, try 89. But in most cases, it's either 87 or 91 that works best.

 

You're right that different octanes don't have an effective difference in power. And yeah, for a car engine designed for 87 (with compression ratios of about 9.5) any octane higher is a waste of money. There's no way for the engine to extract more power.

On engines (like the RX) which ARE designed for 91 (c/r of 10.4 or something) then yes, 91 will produce more power because the computer does not have to retard timing to reduce detonation; thus getting more optimal power efficiency.

If you can limit yourself to accelerating like Grandma, then 87 is the best economical way to go for an RX owner.

But like the manual says, for optimum performance (acceleration), use 91.

 

I wish to admit that the folks who said to use premium in my RX330 seem to be correct. I have a 13.5 mile commute, half city, half highway. On 87 octane I averaged 19.4 mpg.. On the last three full tanks I have used 93 octane(no 91 in Ky.) and have averaged 21.6. Also, the very minor hesitation is gone.

 

It looks like the RX330 does get some benefit from higher octane, while the Rx300 does best on 87 octane.

 

I just purchased my RX330. I currently pump premium but I find myself only getting 15.5-17.5 miles per gallon. I drive both highways and freeways. I hope my gas mileage will improve. I am used to driving like 45-50 on highways and 80-85mph on the freeway. But even with fast driving shouldn't I be getting more miles per gallon? Will lower gas be better? Help!

 

Two problems. Mpg doesn't really start to improve for about 4-5k miles. Also, this ain't no formula one car. Gas mileage drastically drops at speeds over 65-70 because of wind resistance-it's sort of an SUV afterall.

 

You did not answer the question. Hesitation is caused by tranny, not engine. Also Lexus does not require 91 for 1MZFE, refer to RX300's owner's manual you will see.

 

Down in Mexico...you'd better use Premium (92 Octane)...search on my previous posts.

 

don't know about all the scientific stuff, but i personally use premium..i noticed that ever since I've been putting that stuff in my car, it rides smoother and my car starts up easier in the morning..i particularly use V-Power by shell..and sometimes chevron techron. I don't know about increased mileage or that other stuff, but bottom line for me is the car starts up easier and i get better response on the highway.

 

I tried a tank or two of premium and did not notice any difference. Not worth the extra $ to me.

 

This is a very interesting thread. Since we've had our '00 RX300, we've used premium gas (91). I'm not sure why I started using premium from day 1, other than that's what the dealer said was Lexus's recommendation.

So after reading this thread I went to our RX300 owner's manual. And there it was, on page 247: Fuel Type Octane Rating 87 (research octane number 91) or higher. And on the inside back cover: Select Octane Rating 87 (Research Octane Number 91) or higher. For improved vehicle performance, the use of premium unleaded gasoline with an Octane Rating 91 (Research Octane Number 96) or higher is recommended. This is also shown on page 248.

So I feel pretty stupid right now for running premium since 2000. As of today, we're switching to regular 87, unless I hear knocking. If so, we'll move up to 89. Since this is my wife's car, I probably will not be able to compare gas mileage results from 91 vs. 87 octane.

Thanks for the great thread!

 

Congratulations, you are $0.20 per gallon smarter. It is wise to follow User's Manual's recommendation. It is very typical that many owners just assume 91 octane rating is the minimum.

 

I've been using regular in my E46 330i since July and it's quite happy with it. Runs as good as it did with premium.

- GRL

 

...the RX330. However, I do recall reading in the manual that the car will supposedly "run better" on premium. About all I can think of that meaning is the knowck sensor may be able to increase the advance a bit on premium which MAY improve performance and mileage a wee bit. MAYBE!

Anyone ever tried it?

My 330 i got 20.5 mpg city with premium and it gets 20.5 mpg city with regular.