2006 Toyota Sienna and Premium Gas


I have been using regular gas in the Sienna since my wife and I bought it two years ago. No evidence of pinging or detonation.

I was reading the manual concerning the grade of gas to use. The manual neither “requires” or “recommends” premium gas. However it states that premium can be used for “increased performance”.

I’ve decided to try premium to improve the mpg. A ~1 mpg increase would make the cost difference. I was planning to do 3 fill ups (~1000 miles) before checking the mpg. Would this be enough time for the computer to compensate for the premium gas?

Any comments or suggestions would be appreciated.

Ed B.

My guess is that the adjustment will be immediate because it’ll be based on input from the knock sensor. (It had better be immediate when you go from premium back to regular!)

You probably know this, but make sure you don’t use E10 gas for one test and non-E10 gas for the other test, or the results won’t be valid. Use the same station if you can.

Please report back with your findings. This will be valuable input for people in the “recommended” situation who are trying to decide if going to regular gas will actually save any money.

A tank full should be more than enough time for the engine computer to learn, and respond, to a new octane setting. It learns when different octane is used by the signals sent by the knock sensor.

The scan tool maker AutoTap is where you should post your question: http://www.autotap.com

I would say it is recommending premium, but that is only semantics.

You are wise to do a test. It is difficult to tell if you are going to gain any or a lot of mileage advantage. Cars, their condition and your driving habits will all be factored in.

You should not need to wait for three fill ups, I would check from the first and then see if there is a trend as the average octane increases with the next few fill ups. You will also have a more accurate measure by doing three fill ups.

I vote for the three-tank data sample to determine gas mileage. It is tough to know that you filled the tank to exactly the same level each time, and a quart difference shows in the result. I have always used three-tank averages to check mileage.

The caution about E-10 was good. I would not have thought about that.

For several years, I kept a continuous mileage calculation for my '81 Toyota Starlett (best car I ever owned) on a spreadsheet with a graph. That was great because I could see the results of changing tires, tune-ups, etc. Interestingly, that car got BETTER gas mileage in the winter when there was MTBE in the fuel, while most cars were getting worse winter mileage due to the lower energy density in oxygenated fuel. It was a carbureted 5-speed stick. I never varied octane though.

On my wife’s 330 BMW, which insists on 91 octane minimum and recomends 93, I can easily feel the difference of even dropping to mid-grade. I don’t have a really good 3-tank, same load, same weather, same fuel comparison, but the last 3-tank trip to the kid’s college averaged just over 28 mpg. A previous trip using mid-grade averaged about 26.5 mpg.

Thanks for the suggestions. New Jersey uses E10 all year round and I’m getting the gas from the same station. Jersey only has full serve, so I can’t control the amout of gas going into the tank. I just went through the first tank of premium, no noticeable change in mpg yet. I will post back with the results, but it might take a few weeks.


Ed B.

I thought I would post back with the results for the Premium test. Except for 10 gallons, all the gas was bought from the same station.

For 6/16 to 8/7/08 (Premium only)
1225 miles, 61.5 gallons
Trip Computer mpg = 20.4, Calculated mpg = 19.92 The trip computer MPG is usually .5 mpg higher than the calulated value.

For 3/13 to 6/18/08, the van averaged 21.3 mpg over 1850 miles on regular grade gas. However the test period included the annual trip to visit my wife’s sister in Allentown, PA. There’s a lot of hills and with 7 people in the van it tends to kill the mpg. A better comparison would be the same time period last year which also included the Allentown trip.

For 6/18/07 to 8/6/07 (Regular gas)
1844 miles, 92.37 gallons
Calculated mpg = 19.96

As far as I know, New Jersey has been mandating E10 gas year round for the last few years, so I don’t believe this is a factor. In my case, I think it’s safe to say Premium does not make a difference in the Sienna. Note, the Sienna has had no driveability issues in the two years I had been using regular.

Ed B.

If I were to go “mountain climbing”, or if I were a heavy accelerator, I’d use the high octane, anyway.

“Jersey only has full serve, so I can’t control the amout of gas going into the tank.”

I beg to differ. If you tell the attendant that you want the tank filled, and if you prevent him from continuing to pump gas after the pump clicks off for the first time, you will have a tank that is filled, and is not overfilled.

Yes, I also live in NJ and I make it a habit to exit from the car as the tank is being filled. As soon as the pump clicks off, I state, “That’s good–No more”, or if the attendant is Spanish-speaking, I will say, “Bastante–No Mas”. By doing this, I prevent the damage to the evaporative emissions system and its expensive carbon canister that can result from overfilling of the tank. (Avoiding a $300.–$400. dollar repair job is a very good motivation for getting out of the car and thereby preventing the tank from being overfilled!)

If the attendant is otherwise occupied when the pump clicks off, I simply remove the pump handle from the tank myself, print the receipt, and go on my way. Just be sure to remove your credit card from the pump when you take your receipt! I wave my credit card and my receipt at the distant attendant as I drive off into the sunset, in order to prevent him from thinking that I did not pay for my gasoline purchase.