MPG using low octane

some of you may be interested in my little experiment. I used 87 octane in my B200 for a tank and noted that my average gas usage was 7.0L/100km I then
did virtually identical driving using 91 octane (which I'm supposed to use) and found that my milage increased to 6.4L/100km for the whole tank which corresponds to about 500 km. Soooo, seems my milage decreased about 10% and the gas cost is about 10% cheaper for the low octane. The lesson is, and it's been mentioned before but I wanted to confirm, you won't save any money by using low octance but you may hurt your engine.
cheeers, guenter
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Guenter Scholz wrote:

thx for info.
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One experiment going through 2 tanks of gas doing "vitually identical driving" and coming up with a 9% difference in fuel economy may be interesting, but hardly seems proof of anything.
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Trader, where oh where did I say that I claim that this is a 'proof'.... you definitely need to read first. What I 'did' say that it may be 'interesting' to some. re the 'virtually identical driving' well, in view of hyper critical people, I didn't use identical. In fact I did the same road trip in both directions, mostly freeway driving. Elevation diference from beginning to end are nonexistance since they were at sea level and I did fill at Shell stations both times so there is no differences in possible other aspects of the gasoline used other than the octance difference.... make of it what you will, 'I' found it interesting and thought it worth sharing
cheers
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On Aug 20, 8:24 pm, snipped-for-privacy@sciborg.uwaterloo.ca (Guenter Scholz) wrote:

This is what you said:

From the dictionary:
confirm - to make certain or sure, corroborate, verify.
Hence, my reply that two tanks of gas on "virtually identical driving" and coming up with a 9% difference in MPG, is hardly proof of anything. I've seen all kinds of reports, with some people reporting that they thought they got better mileage from higher octane gasoline. Others have reported no difference. And it would seem it could easily depend on the particular engine and gasoline you happen to use. Hence, your statement that your experience "confirms" you won't save any money by using low octane is really meaningless. Show me controlled test data, then I'll believe.
 What I 'did' say that it may be 'interesting'

Did you measure if you had a head wind or tail wind each way? Rule out the possibility that just maybe, while not even knowing it, your driving changed just a bit due to the fact that you knew which gas you had at the time? There is a reason scientists use double blind tests. As to the only possible differences being the octane, that is not true. It's known that some higher octane gas, in addition to the higher octane rating, has a slightly higher energy content. So, the higher MPG could be due to that, not specifically the octane and the next brand of gas may not have the same higher energy content in the premium.

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I tried using low octane in my 380SL and my son said he heard it

Tom Mills -------------------------------------------------------------------------

This is what you said:

From the dictionary:
confirm - to make certain or sure, corroborate, verify.
Hence, my reply that two tanks of gas on "virtually identical driving" and coming up with a 9% difference in MPG, is hardly proof of anything. I've seen all kinds of reports, with some people reporting that they thought they got better mileage from higher octane gasoline. Others have reported no difference. And it would seem it could easily depend on the particular engine and gasoline you happen to use. Hence, your statement that your experience "confirms" you won't save any money by using low octane is really meaningless. Show me controlled test data, then I'll believe.
What I 'did' say that it may be 'interesting'

Did you measure if you had a head wind or tail wind each way? Rule out the possibility that just maybe, while not even knowing it, your driving changed just a bit due to the fact that you knew which gas you had at the time? There is a reason scientists use double blind tests. As to the only possible differences being the octane, that is not true. It's known that some higher octane gas, in addition to the higher octane rating, has a slightly higher energy content. So, the higher MPG could be due to that, not specifically the octane and the next brand of gas may not have the same higher energy content in the premium.

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There is no need to be technical in gauging fuel mileage... head wind/tail wind? Are you kidding?
I once put in 89 octane on my BMW with high compression engine... my average with 93 octane is around 330 miles with reserve left over. I put in 89 octane and my tank is bone dry at the gas station with only 260 miles. I only had splash of fuel when I thought I would have 2 gallons of reserve.
My friend who owns 2000 E320... when he first got the car, he would put in only regular... money was tight for him... his car computer average said 17.3 MPG... he ran it for over a year. Then he switched to 89 and he said it bumped to 20 MPG...
My folk's 2001 E320 always had 93 and the computer said 23.7 MPG... This is 60,000 miles worth of fuel. On long trip of highway only, we get 29 MPG. This we have done it for 500 miles stretch at a time.
Air filter is quite important too. Our SUV with new air filter and high octane fuel gets 19MPG local driving... when the filter is 9 months old, the fuel mileage drops down to 17.5 MPG and will go down to 16 by the year end. This is with 93 octane.
I once filled the SUV with 91 octane from Sunoco... with the fuel mileage reading at 19 MPG with clean filter... the fuel mileage with that tank of 91 octane is 17 MPG.
I don't know how many more types of car do I need to say that will have similar mileage reduction. Generally speaking, look at your compression ratio, if it is high and the manufacturer said high octane is required, then it is required and fuel mileage will drop if you use lower octane.
If you have Honda, Toyota, GM or Ford and all other with 9:1 compression ratio and lower and the manufacturer said 87 is all you need, then 87 is all you need. However, if you put in higher octane, you will see higher fuel mileage.
One lady in newspaper said if she used regular as recommended by Honda, she gets what the car is rated for... 33 MPG, but she put in 93 octane and she got 40 MPG... so calculating cost per mile with fuel only... premium fuel is cheaper to operate than regular because of the extra fuel mileage.
Now, if you are stricty super uber city like NYC only, then I am not sure... but you need to do some experiment yourself for your average driving condition. Not 25 miles highway driving test... heck if you shut off AC and windows up, you will get extra 3 MPG on that same highway test.
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No, you don't have to be technical in gauging fuel mileage. You only have to be technical if you want the results to have any validity.

All those observations are interesting. Surely you've seen just as many posts and observations where people reported no difference in fuel economy. They are interesting too. If you can show me some actual data from a reasonable and carefully controlled test, that would have far more value than the observations of either camp.

I'm not advocating using lower octane than the minumum recommeded by the manufacturer.

That last statement is what I have seen most reputable websites and articles totally disagree with and which I personally don't believe to be true. The overwhelming majority of credible authorities that I have read have stated that if you are using a higher octane than the minimum required, you aren't going to see an increase in MPG. And the science behind it seems relatively straightforward. The higher the octane rating, the higher the resistance to pre-ignition. Therefore, higher compression engines need higher octane. However, increasing octane beyond that, apparently doesn't do anything, except make the customer feel good about buying premium gasoline. If you believe otherwise, perhaps you could explain the science behind it.
Now, I've seen anectodal reports from casual observation go back and forth on this. My main point here is that an observation based on two tanks of driving don't confirm or refute anything. It's just one more observation.

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wrote:

Another important factor is whether you drive east/west in the morning or evening. When driving towards the sun, is gravity will cause less fuel consumption, just like when driving downhill. Also gravity of the moon will play a role.
....just kidding.
When using lower octane than specified, the engine will tend to knock, and the ignition timing will automatically be retarded until knocking disappears to protect the engine. With retarded timing the engine will not run at its optimum, therefor the lower mileage.
A mimimum octane is specified exactly to prevent knocking. The number octane is actually a measure of the ability to avoid selfdetonation. Using higher octane than required does not improve fuel economy, since selfdetonation (knocking) does not occur in the first place (using specified fuel).
Engines with very high compression or with supercharged intake (turbo or compressor) may require higher octane. This is often the case with tuned engines. When using supercharging in street cars, the compression ratio is normally lowered to fit the desired fuel (normal octane).
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Indeed, which is why it is a complete waste of money for most people to buy the "high" octane petrol available at most European petrol stations. The standard 95 is good enough. 97 or 98 octane costs a lot more for no benefit.
The petrol companies' advertising (in Britain at least) is now very carefully calibrated to make no wild claims...e.g. stuff a different mix of detergents is suggested which MAY help some cars run better...
In fact .the vast majority of cars run optimally on 95, as recommended by the car manufacturers.
Shell now mainly seems to want to associate itself with Ferrari, for whom they claim to have developed fuel, and they do this especially with their expensive 98-octane petrol.. The most economical thing to do is to buy a Ferrari baseball cap for the association (for ten or twenty pounds) and fill up with ordinary 95...
95 corresponds to US 91 or thereabouts, AFAIR.
DAS
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A small complementary: Gasoline may also have different energy contents (quality) per volume unit. It is by no means connected to the octane number, but as high octane is used for high performance engines (high compression, highly stressed), high octane may (but not necessarily) be associated with energy contents, thereby giving a bit more power and perhaps mpg.
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A small complementary: Gasoline may also have different energy contents (quality) per volume unit. It is by no means connected to the octane number, but as high octane is used for high performance engines (high compression, highly stressed), high octane may (but not necessarily) be associated with energy contents, thereby giving a bit more power and perhaps mpg.
Higher octane fuels tend to be lighter/less dense and have less BTU content per volume than lower octane fuels.
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Yes, that appears to be one of the truths.
I can see from Wikipedia, that regular gasoline contains in average 34,8 MJ/L, but may vary as much as 4% due to varying quality in the crude oil and in the refinement, whereas premium gasoline contains in average 39,5 MJ/L, not because of higher octane but because of a different quality and composition. As said in average, not necessarily.
From other sources I see, that there is practically no difference in energy contents.
But whith the right engine, you can extract more energy from the fuel. The right engine is one with higher compression, thereby also requiring higher resistance to knocking (higher octane).
In the end, the same engine will normally not benefit from using higher octane than required. Not because of the octane anyway, but maybe because of better quality.... maybe.
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Cheaper gas will not hurt your engine, it will either burn strong or burn weak. The only thing that hurts your engine is your "Friction" and your "Over-stressing" the engine.. Most of you who claim knowing the laws of physics often left out something important. It's almost like a drunken man denying being drunk while he points a finger at someone else.
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On Aug 22, 3:08 pm, "Speeders aren't MURDERERS, Speed saves your

That's certainl ynot true in older high compression engines, without electronic controls and knock detection. Pre-ignition caused by using fuel with too low of an octane rating can destroy these engines. Of course, it depends on how long you drive with it that way, how bad the knock is, etc. It's also not an issue of burning strong or weak.

And your reference that using low octane gasoline in any high compression engines isn't harmful would be? Why do you think manufacturers spec out the minimum octane rating for the cars they build if it makes no difference?
 It's almost like a drunken

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On Fri, 22 Aug 2008 12:51:46 -0700 (PDT), " snipped-for-privacy@optonline.net"

which I've never used and I am happy with the performance and milage and the car has 70k miles on it and I've seen no engine problems and in the lexus forum it's been reported that lexus has said despite the fact that they recommend premium not using it will not in any way damage the engine, I have about 2200 miles in my new SL and I am wary of NOT using premium because of the large engine it has, once I get over it's newness I might experiment a bit. The point is that there is no answer for every car, some cars do need premium and many don't __________________________________________ Never argue with an idiot. They'll drag you down to their level and beat you with experience.
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