Fuel Grades vs. MPG

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blackdiamond

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Today I started an experiment to see how changing my 2004 Sequoia to Premium (92 Octane) will impact the economy. I'm planning to run about five tanks of Shell V-power in a row and see how it compares. I figure the detergent benefits of the V-Power will be a good thing even if the economy doesn't improve.

I know that higher octane can allow the timing to advance yielding a more lean air to fuel ratio, but I also know that the engine managment systems can simply adjust and compensate for just about anything these days.

I've only driven a few miles so far, but it was interesting to see that the average mpg on the trip computer is higher than normal. The ironic part is that I know for a fact that it isn't possible for any fuel grade to make as much difference as I'm seeing so it must be the result of a lot of "down hill" driving.

Any thoughts on if I'll see any improvement? When fuel prices were really high I calculated that I only needed to get 1 mph better to justify the additional cost. Assuming the $0.10 steps in fuel prices, the effective cost for premium gets lower and lower as the prices rise. The % increase for premium goes down. Right now the local stations are exceeding the old $0.10 standard.
 
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I like your idea about running 5 full tanks to get an average. You/we need to know the SD to draw any conclusions. When I report mileage on my vehicles I do the SD also as it yields valuable information for the reader.
 
The standard answer is, if it was pulling timing due to knock with the lower octane, you will see a gain. If it wasn't pulling timing, you won't see a difference.

What is it spec'd for?
 
I almost always run either 76 or Shell gasoline. Both are Top Tier fuels. The V-Power premium grade has significantly more detergents than the lower two grades, I would assume that 76 would be similar but have never found any documentation. This is why Shell advertises that V-Power actively cleans, but they don't make the same claim for other grades.

In the past I've generally gotten slightly better mileage with 76 fuels so Shell should be the conservative one.
 
I ran the number tonight and for the premium to pay for itself at the current prices and a $0.25 spread in price I'll need to see a mpg improvement of about 1.5 mpg which is almost 10%. I'll give it an honest try, but I'm not anticipating seeing that much of an improvement.
 
Originally Posted By: blackdiamond
I ran the number tonight and for the premium to pay for itself at the current prices and a $0.25 spread in price I'll need to see a mpg improvement of about 1.5 mpg which is almost 10%. I'll give it an honest try, but I'm not anticipating seeing that much of an improvement.


I'm curious to see how this turns out since it's rated for regular.

1.5mpg is definately doable if it was pulling timing. I've gained up to 5mpg many times by going with a higher octane in the detonatoin prone TL.
 
Does the fuel your buying have ethanol blended in?
Ethanol in all grades?
I get a mileage boost from V power in my Caravan (spec 87 octane) but I think it is mostly because the premium (in my area)has no ethanol.
The mileage boost doesn't offset the premiums price in my case.
 
According to "Experts" of some car manufactures, there is no gain in performance or mileage for using premium grade in cars designed for regular.

http://www.usatoday.com/money/autos/2003-07-30-premiumgas_x.htm

Excerpts:

No data show that engines designed strictly for regular run better or longer on premium.

The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."

"There is no way of taking advantage of premium in a regular-grade car" says Furey, a chemist and fuels specialist at General Motors

"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.

"No customer should ever be deluded into thinking there's any value in buying a higher grade of octane than we specify," says Toyota's Paul Williamsen, technical expert and trainer.

-----

I tries regular grade in '94 Lexus LS400 while going to Vegas in a summer long ago, the recommended grade is premium (91 octane), the car had problem accelerating up the steep hills at Death Valley when the temperature was 120+ F. Around city and flat highway I did not detect power lost with regular grade. The gas mileage is about the same for both regular and premium.

The other two cars still use premium are '00 E430 and '04 S2000, both cars are recommended premium grade, because I can feel substantial differences in performance when using regular versus premium gas.
 
BuickGN is correct. You'll only see a difference if your car has a knock sensor. If your car has no knock sensor, and is specified for 87 octane, you're wasting your money.

Does your car have a knock sensor? What fuel is specified in yor vehicle?
 
Even if you have knock sensor, do you know the algorithm ECU uses to advance the timing? I would think that once it hits pinging, it retards the timing. The question is, when does it attempt to advance the timing again? Engine does not know when you fill the tank with premium. Does it try on every restart? What is the rest period before trying to advance the park?

- Vikas
 
Originally Posted By: Vikas
Even if you have knock sensor, do you know the algorithm ECU uses to advance the timing? I would think that once it hits pinging, it retards the timing. The question is, when does it attempt to advance the timing again? Engine does not know when you fill the tank with premium. Does it try on every restart? What is the rest period before trying to advance the park?

- Vikas


In the cars I've had on the scanner it puts timing back in within a second or so. That's why you'll notice a surging when it's pulling a lot of timing and the putting it back in.
 
Originally Posted By: blackdiamond
Oh, the Sequoia is rated for regular grade fuel.


If your manual does not state something like; 91 octane or higher recommended,or premium only, you may not get any gain in anything.so we`ll see.
 
You might see a difference. My Isizu recommends 87, when I add mid grade (89), I get an extra 1.5 MPG; not much difference from 89 to 91.
 
Originally Posted By: Vikas
Even if you have knock sensor, do you know the algorithm ECU uses to advance the timing? I would think that once it hits pinging, it retards the timing. The question is, when does it attempt to advance the timing again? Engine does not know when you fill the tank with premium. Does it try on every restart? What is the rest period before trying to advance the park?

- Vikas


I doubt many people know this information about their automobiles. I've considered disconnecting the battery to eliminate any learned fuel curves, but I didn't notice any difference in the way the motor ran when I disconnect the battery in the past.

My 2000 SS Camaro would barely idle after the battery was disconnected because it erased something related to the fuel mapping. People would do this before drag racing because they would get better times, but the car would eventually revert back to where it was programed to be.

Five tanks should be about a $27.50 gamble figuring a 22 gallon fill and a $0.25 price difference so it's not the end of the world either way.
 
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