Hey - just thought this was interesting. As many of you know here in ON we're mostly stuck with 91 octane. I've been in NY state a lot lately so I've filled up with 95 twice. Oddly, I've noticed both times I got ~200km less per tank - same style of driving, same highway/city percentage, nothing has changed (tire pressure is the same etc..). Anyone else notice the higher the octane the less mpg you get? I normally get between 570-610km per tank with 91. I got 418km and 425km these last two tanks with 95. I didn't notice any difference in power, either. Nutty, I know.

 

I thought the basic principle of higher octane gas is that it burns slower = more mileage? That is strange. How about giving Sunoco 94 a shot? Then again, gas prices are quite high right now so 94 octane will be even more expensive

 

Isn't it that the highter the octane the better/more efficient the burn? I was told to run a higher octane if you do alot of city driving
It makes sense since you would pull higher HP using higher octane fuel.

I've always run Sunoco 94 in all my cars so I can't really say if there is a difference in milage.
For a full tank I usually see around 600km's on average( city/highway mix). My car is a 2003 with 54Km on her.

Bill

 

Right - I thought the basic premise was the higher the octane the better the mpg, so it was weird to see such a drastic drop in mpg with 95 octane. I have used Sunoco 94 and I noticed it was pretty much the same as 91 (~600km per tank) in my car. My car is an 03.5 with 40k miles, I've put 15k of those on it and I get 600km per tank almost religiously. I only posted because I was so surprised that 95 would net me such a decrease. My driving is about 60% highway/40% city.

Anyway, not a huge deal. I will jsut continue using 91 or sunoco 94, just thought it was interesting.

 

Octane is something that inhibits combustion. So the higher the octane, the harder it is to ignite.

But because of that, engines running higher octane fuel can run more timing advance in spark or more boost since the fuel is less likely to pre-ignite, or ping, or pre-detonate (choose your term).

So I'm guessing in theory, a higher octane fuel, if the engine management system can't take advantage of it, will cause a greater fuel consumption as more throttle is needed accelerate at the same rate.

Probably, the engine is designed to only advance the timing so far, so running a higher octane fuel won't make the engine advance the timing and thus take advantage of the fuel. That's why you don't feel much difference with it.

At least that's what my thinking is. Anyone else wanna chime in?

 

I think you're bang on. With other vehicles I've owned that had 91 recommended and not required I noticed a fuel efficiency increase with premium versus 87. The engine managment must have been able able to make use of the higher octane.
On other vehicles requiring only regular it made no difference or slightly decresed my mileage. Since 91 is the only high grade available here I can't comment on the G difference since it requires only that grade minimum.

 

that's pretty much how i understand it. higher octane does not equate to better gas milage... in fact, when i had my Mustang, higher octane that 89 actually made it less fuel efficent.

 

I had analys one month (October) using Sunoco Octane 91 vs one month (September) using Esso Ocatne 91, i find that Esso gas gives a better milage and better performance as well. Same style driving and I really can't explain why Sunoco gives me lower milage than Esso, but for sure I can feel the difference in performance wise. Yesterday I decided to stop using Sunoco and use Esso....boy, it sure does feel the difference.

Has anyone try the experiment between Esso and Sunoco fuels?

Thanks
Sandip

 

One trick to raise octane is to mix Ethanol with gasoline. Ethanol has a higher octane rating, and burns cleaner then gasoline. However, ethanol contains 30% less heat energy when burt then gasoline, so your miliage WILL decrease per gallon when using a fuel mixed with Ethanol.

Ethanol blending is becoming very popular because the governent offers tax credits to the oil companies who mix ethanol. This is good for the government because, in America, ethanol is blended from corn, which the goverenment subsadizes.

Or maybe the ECU just isn't adjusting, who knows?

 

Picus112, I'm in agreement with peeps here that the higher the octane, the more inhibited the burn, but asuming the higher octane will allow higher performance, that performance won't exceed the factory specs on timing....which for the Sedan is 15 degrees + - 5 degrees., so using a higher octane than needed is not necessarily a good thing, and might even be bad.

The manufacturer recommends 91 octane and it's been determined that a lower octane can be used, but 91 is supposed to give the best performance.

Personally I think to exceed that (91) could be detrimental to performance and gas mileage, and not better as was always thought.

Another possiblility is that the gas in the U.S. is not made to the same standard as ours and has a different octane rating, and also you may find that a lot of their gas down there has alcohol in it. What do they call that -- Gas-O-Hol????? -- which might not be as efficient, and yield as much gas mileage as our pure gasoline.

Just a thought.

Checking mileage with our 91 octane gas again now will answer that question.

Let us know what develops.
C.

 

this is interesting... i bought my car in Tennessee, where highest octane rating is 93. then i moved to California, where highest octane rating is 91. i wonder if my car was specifically tuned for 93 octane gas, since it was shipped to TN, and if 91 octane in CA is messing with the tune...

 

/me watches thread

 

When was this because there are two possible explanations. I believe you ised 93 octane not 95 because more often then not, 93 is the highest readily available except for some Sunoco's which carry 94.

Now, I don't know if every state has to abide by this or not but in NY, they change the gas in the winter I think between October -April they put this oxygenated crap in the gas which is supposed to provide lower emissions however the morons don't realize you actually burn more gas! I believe this is our last winter with it as they know have found it causes cancer or sumtin. Anyway, without fail in all of my cars, once the gas staions have this oxygenated crap, MPG goes way down!!! I am going out on a limb by thinking that where you got gas got an early batch of this crap!

The other reason is being that it got colder, you can be running less PSI in your tiures without knowing it.

That's all I can think of because anytime I put high test in my truck (every so often) I get much better mileage over regular!

 

The manufacturers change the gas up here in Canada too, and it's to add gasline antifreeze as well as oxygenate the fuel.
.......but I was told that doesn't happen (here) until late November......??????

Soft tires will cause more fuel consumption, and I've read recently that a tire underinflated by 10 psi, can reduce your mileage by 3 mpg's!
I do know from my experience that cold mornings cause longer warmups and lousy mileage. And the colder the weather, the worse it gets.
C.

 

Colin, I think the gas here starts to change about the end of this month but may vary by brand. I'm going to check it out.

Yep, the cold weather wreaks havoc with the mileage that's for sure. Longer warmups, more idling more driveline friction, even rolling resistance on the bad stuff!