why does the 2004 Totota Avalon use high test gas

I don't think I said that you cannot tell the difference. What I said was the the difference was not because the gas changed the variable valve timing. If there is a difference, it's because the knock sensors changed the ignition timing.
I'm not sure that you can feel the difference, but assuming you can, you don't feel for the reason you think. That's what I said.

I gave you the formula to figure this out for certain. If you get better mileage by about 0.75 mpg when using premium, then premium is cheaper. The break even point in the cost per mile comes at about 0.5 mpg, so if you get better than that then you are paying more to use regular than to use premium.
If your car calls for premium, or mid-grade, and you use regular instead, then the ignition timing is retarded to prevent knock, this retardation of the timing cuts performance and reduces the fuel economy. If you figure out how far the fuel economy is reduced, you can calculate what the cost is. The higher the price of gas,the better off you are using the higher grade of gas. If your car calls for regular, there is no benefit to using a higher grade. But if your car calls for the higher grade, there is a dollar cost to use a lower grade.
You live in a false economy. Do the math.
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Of course he lives in a false economy. He keeps quality with octane level, because all he knows is that bigger numbers must mean better.
And then when he sees the price, all he knows is that cheaper to buy must mean cheaper to run, because smaller number.
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On Saturday, November 1, 2014 7:33:59 PM UTC-5, Jeff Strickland wrote:

I've already done it several times. And quite accurately too, being as it's on the highway, I have trip counters, and I can do math. The difference in mpg between premium and regular in my car is so small it's not an issue. If I run premium, it's purely for the small increase in performance. Why do you keep insisting I do something I've already done several times? Sheesh.. it boggles the mind.
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Because if you really did the math, you would not use regular in a car that wants you to use premium. And, if you could feel the difference "at idle" asw you claim, then your math would hae to prove that premium is cheaper to use than regular.
What you do is not supported by what you say, and what you say means you would not do what you do. You would not insist that you feel the difference at idle, then take a road trip and use the lesser grade of gasoline. You would not claim to have done the math and then use the lesser grade of gas. You make mixed statements and wonder why people say you are nonsensical.
With a \$0.20 difference in the price of premium over the price of regular, all you need is about 0.5 mpg to 0.75 mpg difference to break even, and my car gives me almost 3 mpg when I use premium instead of regular. My car does not even require premium, it requires mid-grade but they do not have mid-grade at Costco and the premiuim that they carry costs the same as the mid-grade at the gas station down the street.
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The topic is, why does my car require premium? with a follow up question, can I use regular instead?
The OP requires premium, and you are off on tangents that do not even apply, and you are on them for days! Holy shit!
You do not feel any difference, and any difference you do feel comes from the drugs. Your car does not need, nor does it appreciate, premium fuel.
The OP has a car that requires premium. Everything I have said is true for cars that take premium but the operator uses regular instead. Nothing I said is true for you. Sheesh!
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Jeff Strickland wrote:

I contend the OP does not need premium. I have the same car and it only requires regular.
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I don't know what he needs. If he says there is a sticker on the gas cap or an admonition in the manual to use Premium, then I take him at his word. Assuming he is right, there are benefits to using Premium and costs of not using it.
There is no benefit to using premium if it is not needed, but if the engine needs it then there is a cost in not using it.
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Jeff Strickland wrote:

I have the same vehicle except it is one year newer. My manual says Regular octane 87 gas is required and Premium gas octane 91 is recommended for higher performance.
Seems to me the manufacturer has already determined what type of gas the car needs. It also has determined that better gas gives better performance.
Haven't you always suggested to go by what the manual recommends? Here's an opportunity for you to examine your own preconceived notions.
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Premium gives better performance, which Toyota admits, because the timing is set to the most advantageous position. They do this through the ECU. The car can tolerate (requires) a minimum of 87 octane. It (the ECU) alters the ignition timing to retard it enough to prohibit engine knock, this also reduces performance, which Toyota admits. Retarding the ignition timing happens because the knock sensors detect the knock and tells the ECU, which retards the ignition timing to eliminate knock.
If they say that you can get better performance from Premium, then by definition it gets lesser performance from Regular. The minimum requirement is Regular (87 octane), but for better performance use premium. Premium is desired, regular is the minimum. Premium is the recommendation, Regular is the requirement. THAT'S WHAT YOUR BOOK SAYS.
This brings me back to calculating COST PER MILE. Even though a gallon of premium costs more than a gallon of regular, the improvement in mileage can result in a lower COST PER MILE. Over the course of a year, an increase of 3 mpg can save \$150 on 10,000 miles. Since they "recommend Premium for higher performance," then the car actually wants premium. It tolerates regular, it wants premium.
If the car did not want premium, they would not put in the part about, "for better performance..." If the only gas that the car WANTS is regular, they would not tell you to get better performance by using premium. Instead of telling you to use regular at a loss, they tell you to use premium for a gain. Getting a gain by using X is the same but opposite as suffering a loss by using Y. Getting a gain is a positive, suffering a loss is a negative. They start at the bottom and tell you how to get better, but they could start at the top and tell you that less is okay. You must use at least Y, but you will get better if you use X instead. You must use 87, but you can get better performance if you use 91.
I'm saying that if you ran a test of several tanks of premium, and logged your mileage, you would find that the cost per mile would go down -- making premium cheaper to use. If it is not cheaper per mile, then stop the test and revert to regular. My limited experience is that premium will give you 2 to 3 mpg better mileage, and this will offset the higher price of premium, resulting in a lower cost per mile to operate your car.
Use 91 and run the numbers. You should find that 91 costs less.
If you drive a Tercel or Corolla that does not benefit from 91, then don't bother testing. Test if you want, but you should discover that there is no benefit.
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And not just any 93 octane gas, either. Use only a Top Tier supplier, such as Shell or Costco (toptiergas.com), just like Toyota recommends.
10 years ago I had a 94 Lexus ES; after running a few tanks of Shell 93 through it to clean things up, it started getting 3mpg better even on Shell 87. Yes, Virginia, there is a difference in fuel suppliers.
Don't use grocery store gas.
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Jeff Strickland wrote:

I decided to test this. I have a 2004 Toyota Avalon XLS just about to go over 100K miles. Since I've owned it for three years I have used nothing but Regular gas. Typically I get 20-22 MPG driving around town. If I drive it the MPG will be higher than if my wife drives it since she has a lead foot. Highway mileage is about 28-30 MPG, maybe higher if I just use cruise.
The last two fillups I have used Premium 93 octane. The car has averaged 22 MPG during that time driving around town. We have had a cold chill here in SE VA so I'll give it the benefit of the doubt and say maybe it would have gotten 23-24 MPG. I haven't noticed any perceptible difference in performance, but I don't typically gun it unless I must get into traffic. Even then it already has more than enough power without complaining.
A typical fillup is around 18 gallons. Today the Regular gas was \$2.69 and the Premium was \$3.19. That's a difference of \$0.50. I have seen differences of \$0.40 at other places.
Paying \$0.50 extra per gallon (\$9.00 tankful) doesn't seem worth the extra 2 MPG (36 tankful) to me. Maybe if I was getting a difference of 4-5 MPG I would consider switching, but I can't justify the higher cost for such minimal gain.
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...unless you consider satisfying his inner urge to believe that "higher octane is the good gas" to be a benefit.
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snipped-for-privacy@wt.net wrote:

There you go again, equating the gasoline's quality with its octane rating.
There is no difference in quality, PERIOD. There is a difference in octane rating. There is zero connection between octane rating and quality.
You just really, really, really want octane to equal quality, and a higher octane number to mean a higher quality. You can't accept anything else.
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On Monday, November 3, 2014 4:39:55 AM UTC-6, Elmo P. Shagnasty wrote:

Yea, I did it purely because it seems to chap your whiny ass. Looks like I succeeded, as again you are having a hissy fit over basically nothing. chortle..
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snipped-for-privacy@wt.net wrote:

you'd like to think that, but your continued actions show that you really really think "higher octane number" equals "good gas" and "lower octane number" equals "bad gas".
That right there is enough proof for anyone that you really don't know what you're talking about--including your psychosis that "my car runs better on the good gas".
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but it leads his frame of mind and his argument.
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On 18/10/2014 3:18 PM, Dutch wrote:

It might be an ethanol issue. Premium gas sold in Canada has no ethanol alcohol added or blended.
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