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ycr99

Grade Of Gas

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I use the cheapest unleaded available. (I'm poor, what can I say)

 

I have heard though, that using a higher octane of gas can improve your mileage. Is it true? If so, I might try it. If not, then I'll stick w/ 87

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trap
I use the cheapest unleaded available. (I'm poor, what can I say)

 

I have heard though, that using a higher octane of gas can improve your mileage. Is it true? If so, I might try it. If not, then I'll stick w/ 87

I have also heard that, but never tried it. I am also cheap (ok, I spend my money other places) and put in the cheapest octane gas at the cheapest price I can find. I know you could get better gas mileage and also a better running engine with the higher octane, but is it worth the extra expense? - I don't think so. That's just me.

Edited by Bikeman982

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my friend documented his fuel mileage, fuel trims, and octane rating of fuel over a 4 month peroid.

 

there was NO difference between octanes and fuel mileage. octane rating is ONLY refering to its resistance to knock and nothing else.

 

infact it is possible to LOOSE milage with a high octane fuel because its possible that its not all igniting (unlikely with the corolla's head/chamber designs). just run 87 octane unless you've done some sort of modification to the engine that requires a higher octane fuel.

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My 2000 corolla manual recommends octane 87 and higher, so I assume there is no ignitability (is that even a word?) problem in corollas. I have been exclusively using BP Amoco Silver octane 89, it costs $2.379/GAL here in TN. The octane 87 is 10 cents cheaper, so I could be saving of around $1.30 per tank, but then again, I dont fill up more than once a month, so I dont really care going cheaper.

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So the concensus is that higher octane fuel will be better to reduce engine knock but does nothing to improve gas mileage - then I will stick to buying the lowest octane, cheapest gas I can find.

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You will really never find out for sure if you will get better or worse fuel economy unless you try for yourself. Technically, if you car recommends regular gas - just by switching to a higher grade will not automatically guarantee better or worse mileage - many factors come to play: how old is the engine, how many miles, how was it maintained, what are its tolerances, driving conditions, quality of gasoline in the area, etc. Generally speaking - if a car is well tuned and does not show any pinging or drivability issues with regular gas - you should not see any change in fuel economy with a switch. Some cars may get worse mileage with higher octane some better - hard to say which cars or what circumstances. Just the way it works out.

 

I'm one of those cases where I get better mileage with higher octane. Not just one or two tank fulls - I run around 7 or 8 tanks of each grade (my commute is about 400-500 miles a week - so I fill up often) and average over the bunch. Then switch gas station brand after running the different grades at one particular gas station. I also duplicated this with another vehicle and different driver to eliminate any favoring one way or the other.

 

What I found - I consistently got 2-3 MPG with each step up in grade. But I still have to watch the price of gas - as the price of gas goes down - I save more with higher octane. As it starts going up (break even point was when the gas was over $3 a gallon).

 

So what does an extra 2-3 MPG per elevation of grade get you, This is what I got:

 

I ran my test just because - there was a lot of armchair posting in various forums, I needed to see for myself. Taking average cost of gas over the 22 weeks of testing as around $2.40 (high of $3.30, low of $1.95).

 

With 87 I got between 30-32 MPG, 89 got me 32-34MPG, 93 got me 34-36MPG - all consistently (averaged over several tanks for more "realistic" numbers - started with 87 and worked up, temperatures pretty consistent (avoided too much temperature extremes and times of "winter gas" in my area).

 

Cost of operation with 87 octane ($2.399) - $0.0773 per mile

Cost of operation with 89 octane ($2.499) - $0.0757 per mile

Cost of operation with 93 octane ($2.599) - $0.0742 per mile

 

As you can see - seemingly very little difference when you look at costs per mile. Multiply the effect over 10K miles - you save a finite amount of money. From the above figures - I basically saved enough for another tank of gas in around a 10K period of time, almost three tanks of gas over a year for me. Similar results for the other car - mileage runs from ~129K miles on the Corolla, almost 50K on the Matrix.

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I probably don't buy enough gas over the year to make any significance in savings. I think I will continue to use the lower octane, cheapest gas available. My car does not knock and it seems to perform satisfactorily with the gas I am purchasing. I think the best way to make a significant change in my mileage is to slightly alter my driving habits and try to be a conservative driver as well as use my car more for highway and less for around town. Time will tell.

Edited by Bikeman982

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Only put higher octane gas in cars that need it. A Corolla isn't one of them. If your manual says 87 or higher go with 87. We've had a couple of cars that said "Premium Fuel Only, 92 octane or higher" Some of them, like the Lincoln could get away with 87, although fuel economy was less. The Contour SVT really needed premium because its performance was adversely affected by regular, and we bought the car for its high performance.

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Do not use gasoline of a higher octane than the owner's manual recommends. The use of a higher octane gasoline in a car without the proper compression and timing will cause carbon fouling in the combustion chambers. THere is absolutely no reason for using anything higher than what the manual recommends.

 

I also do not buy the above poster's claims of progressively better mileage with increased octane in a Corolla, and instead would attribute any perceived gains to 'gentler' driving and the associated increases caused by 'trying' to get max MPG with the higher octane fuels.

 

On the other hand, cars that REQUIRE 93 octane probably will experience LESS MPG by using less than the recommended octane.

 

Do not believe you are doing your car a favor by using 'unspecified' fluids, including gasoline.

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I'm just curious Fishexpo101, did you track these tests on the Corolla with stock wheels or aftermarket plus size wheels? It would be interesting to see the results with both wheels options.

Edited by Silver Bullet

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After driving more highway miles than normal, I filled up my tank and this is what I got. I put on 294 miles and used 10 gallons of gas. That means 29.4 miles per gallon, right?

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I'm just curious Fishexpo101, did you track these tests on the Corolla with stock wheels or aftermarket plus size wheels? It would be interesting to see the results with both wheels options.

Those were with almost stock sized wheels (Plus zero upgrade) on alloys. I ran 16" alloys a few years ago and generally got slightly worse fuel economy all around. No doubt due to the wider wheel profile on the 16" wheels. Also ran the test during that time - but did not notice much difference, if any, with higher octane gasoline at the mileage at the time (~30K miles). Now with more miles on the clock, I notice finite fuel gains with the more expensive fuels. Also note that this was on the 1ZZFE Corolla (2ZZGE Matrix gets premium regardless), 10:1 compression, and knock sensors - the ECM will take advantage of the higher octane and modify timing accordingly. A MINIMUM of 87 Octane is recommended for the Corolla - their computer is smart enough to adjust timing to optimize the combustion. Some others cannot and will suffer from anything from overheating the car (unburnt fuel sent to cat) to emissions related issues.

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A MINIMUM of 87 Octane is recommended for the Corolla - their computer is smart enough to adjust timing to optimize the combustion. Some others cannot and will suffer from anything from overheating the car (unburnt fuel sent to cat) to emissions related issues.

 

There was an interesting post on http://9thgencorolla.com/forums/portal.php a while ago.

Someone with OBD2 interface plotted timing advance vs RPM on 2 runs: one with 87 and one with premium gas. The curves overlapped almost perfectly. There was no evidence of changed timing.

Now, if your engine is carbonized badly, there could be a difference.

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Very interesting post - some people have noticed different timing, fuel trims , etc. - others get zero effect from changing octanes. Probably due to so many variables that has to be dealt with. Would be very useful if the person on 9th gen monitored this for a few months to get better averages. A one tank shot has too much variability in it to put too much faith into - but a neat test none the less. I'll have to double check for myself in the next few months with my scanner. Nice link.

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