There has been a long standing debate on is it worth using 91-octane gas over 87-octane. Well, to solve that I did a lot of researching and some experimenting. Check it out at The misguided fear of premium gas

SPOILER: In my 2007 Lexus RX350, I had a lower cost per mile using 91-octane over 87-octane. More and more cars today are being designed to utilize premium gas and many will actually save money using 91-octane over regular gas. With the cost of premium being only 20-cents (which it pretty much has been for a long time), the incremental cost per tank is a much smaller percentage in cost for a bigger return in distance.

Interested in seeing what others think and any suggestions for additional test.

James

 

I try to maintain the recommended 91 octane gas by alternating between 89 and 93 at the halfway mark on my fuel gauge. In my area the common grades are 87,89 and 93 octane. On a recent 1000 mile trip that was all freeway driving I avg 26 mpg driving at 73 mph. I was pleasantly surprised since I was expecting the advertised 23 mpg highway. I believe the article especially with our high compression engine.

 

That article reinforces what I've found to be true on my RX.

 

interesting. be prepared for attack by 'experts' that will take offense at anybody advancing a point of view that differs from their truth.

 

Yes- people have to do the math. It's the cost per mile, not mile per gallon. MPG is only part of the equation.

Now that's a trivial expense really and there are other benefits with premium which include smoother idle and better acceleration. (both subjective really, your butt dyno can't quantify the difference) The math will probably prove that premium is not a detriment to your pocketbook.

The message? Do the Maths!
Cost per gallon/MPG=cost per mile.

Check it out.
Premium
MPG = 23
Cost = $4.10
Cost per Mile = $0.1782

Mid Grade
MPG = 22
Cost = $4.00
Cost per Mile = $0.1818

That's a virtual ROI wash.
If fuel stayed the exact same price the entire time you could drive 12,000 miles here's the breakdown.
Premium would have cost you $2,139.13
Mid Grade would have cost $2,181.18
Total savings? $42.68

 

In a weak moment I recently filled up with 87 (40 cents cheaper than 91 octane). And everything seemed normal, except that I could hear knocking when accelerating onto the freeway. So, 87 is too low.

I have been routinely using 89, and do not hear any knocking. My understanding is this, if the engine knocks the knock sensor will retard the spark and leave it retarded--lowering engine efficiency. If no knocks, it will advance the spark to where it should be. So my theory is to use the lowest octane that never knocks, which seems to be 89 in my RX.

Of course, it I were hauling a load or planning a trip to the mountains, I would fill it with 91.

 

is this for exclusive for the RX350? My RX330 doesnt say it requires premium neither on the fuel door.

 

As Chpsk8 explains the difference between using 87 and 91/93 is very minimal when you compare the gas mileage you get.

I have always used 93 mainly since its harder to find 91, becuase the difference is cost is only about ~4 bucks which is pretty negligible.

I get beef from some of my friends that why would i fill it up with premium since it cost so much....Then I explain the difference and then they are like...thats it.....then they are all fine about it...

IMO 91/93 is the way to go. If you are going to buy a luxury car dont cheap out on 4 bucks!

 

Jeez, I didn't know this was a Luxury car! It is just a small suv on a Camry frame.

If I had a 911 sitting in the driveway, there would be no argument. But an RX350? It is worth cheaping out some!

 

I've taken to using nothing but premium with our 05 RX. The butt dyno tells me that it makes more power (especially in our mountains), the read out tells me it gets better mileage. I've also calculated my mileage using the old tried and true method of miles driven divided by gallons and that actually gives me a slightly higher MPG then the vehicle read out. At any rate, figuring cost per mile, I actually come out slightly ahead using higher octane. Don't need any more convincing than that.

 

RX330 does not require premium, but mileage will improve using it. From what my Lexus service tech has said is that the RX350 does require premium.
Those of us with 330's have a choice in what we use. I've run all three but not enough to make a conclusive decision what is best for me. Another few months of data and I'll know what I'll keep putting in. So far nothing earth shattering with any of the octanes.

 

The 2004 RX330 manual states:In my 04 RX330 I get about 1.5 MPG more with premium. I also have access to real gasoline (no ethanol added) and that also improves my mileage by 1.5-2 MPG.

Another factor for me is that when I have tried regular my car would smell of rotten eggs under moderate load. This doesn't occur when I use premium.

 

Not only will this be a better economically in the short term at the pump, it *may* be economical in the long term at the shop...

 

Do you guys think it is better to spend extra $ to get Shell or Chevron gas ove the discount Marathon, Mobil or Citgo fuel? I am skeptical about Shell' claim in commercial that their fuel reduces valve gunk build-up.

 

I burn premium from any of the Top Tier suppliers. Usually Shell but Citgo is a Tip Tier supplier too. I usually avoid Citgo for political reasons. I don't care to send money to Hugo Chavez.