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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #101  
Old 02-13-2013, 04:36 AM
granlund granlund is offline
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Quote:
Originally Posted by cn90 View Post
On the same topic, does high-octane fuel offers more mileage?
The question is $ spent per mile.

Let's say octane 87 is $3.50/gallon.
Let's say octane 91 is $3.90/gallon.

With an 18-G fill-up, the price difference is $7.20.
But if octane 91 gives us more "energy density", i.e., more Joules per kg of fuel, then itmakes more sense to use 91.

Does anyone have any data on $ spent/mile on different octanes.
Higher octane/AKI gasoline actually has slightly less energy density, believe it or not. The difference is the engine's ability to extract energy density from the fuel. An engine designed for higher AKI can extract a net higher energy density from higher AKT than lower AKI.

At some point I should use my live monitoring OBD2 and check ignition advance on the highway with both 87 and 91.

Last edited by granlund; 02-13-2013 at 06:45 AM.
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  #102  
Old 02-13-2013, 06:38 AM
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Studawg Studawg is offline
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Quote:
Originally Posted by franka View Post
and more energy per gallon than gas.
This nonsense was posted on the first page of this thread, and then that poster went on to make many more comments. This is false, and the opposite is, in fact, true. This information is so patently false that it would seem someone with a particular agenda had to start this for it to be out there. I mean, how does information that is this utterly WRONG get out there and then picked up? I know that this post was a couple years ago, but I thought everybody knew this 5+ years ago.

The difficult part about quantifying 87 vs. 89 vs. 91 etc...is the problem that is ethanol. To get any sort of real world information, you have to have a control. If one doesnt have access to pure gasoline, (which everyone used to) they are only guessing at the percentage of ethanol in the fuel. There have been recorded ethanol contents in fuel samples ranging from 5% to 20%. (It has been proven that E15 will do damage to modern, as in new engines, even before phase separation.) So you have to test it, and there are ethanol test kits that you can purchase. The higher the ethanol content in the fuel, the lower MPGs you are going to get, you can bank on that. Ethanol will raise the octane of gasoline, so what happens is, distributors start by adding ethanol to 85 octane gas to get 87, then add even more to get 90, 91 or "premium" and charge more for it. This is why pumps say "gasoline contains up to 10% ethanol.

Then, at a certain time, the ethanol begins to phase separate and you are left with 85 octane gasoline (if you put in 87) in your tank, 100% ethanol and water, with the water and ethanol mixture sitting below the gas, then sometimes a layer of pure water at the bottom. The longer the ethanol blended fuel is in your tank, the worse this problem is. The problem is also exacerbated when the vehicle in question is stored outside, compared to being stored in a garage, due to temperature and humidity.

When it comes to MPG, trying to quantify which octane rating to put in your gas will be hard due to variations in ethanol content.

For my car, its nothing but 91+ octane pure gasoline.
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  #103  
Old 02-13-2013, 02:25 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by granlund View Post
I should use my live monitoring OBD2 and check ignition advance on the highway with both 87 and 91.
THAT, would be very useful because otherwise, we're all just guessing (including me).
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  #104  
Old 02-13-2013, 02:27 PM
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Quote:
Originally Posted by granlund View Post
Higher octane/AKI gasoline actually has slightly less energy density, believe it or not..
I understand the sentiment (remember, they inject water, I'm told, to prevent pinging in race engines,and, we all know high-octane jet fuel is basically very clean kerosene fuel oil) ... but still ... I have to go back to the octane FAQ, which clearly says:

Quote:
"Antiknock ability is _not_ substantially related to 1. The energy content of fuel."
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  #105  
Old 02-13-2013, 04:44 PM
professorman professorman is offline
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....

Last edited by professorman; 02-13-2013 at 04:51 PM.
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  #106  
Old 02-14-2013, 09:45 AM
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Not sure if this is BS or not, but my cousin works for state government and said when his agency tests octane ratings at the pump, they only test for the minimum. Therefore, the actual octane rating (for example 87) is generally higher. He's convinced 87 octane is almost always closer to 89-91, depending on where the fuel came from.
Anyone else ever hear this?
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  #107  
Old 02-14-2013, 12:18 PM
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aa240sx aa240sx is offline
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Very timely conversation. If I had the time to do a scientific study to really determine mpg using 87 vs 91, I would too, but like most of us I don't. What I do take away from this thread though is that you can use 87 without ill effect as long as you don't have a lead foot.

Given that gas is now over $4.00/gallon for 87 at least in the SoCal area, I think I will now switch from mid-grade usage. I have a feeling a lot of people are going to start doing this.
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  #108  
Old 02-14-2013, 10:57 PM
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Quote:
Originally Posted by aa240sx View Post
If I had the time to do a scientific study
It looks like the exact study we'd want was already done:
- CRC PROGRAM FOR QUANTIFYING PERFORMANCE OF KNOCK-SENSOR- EQUIPPED VEHICLES WITH VARYING OCTANE LEVEL
Quote:
Originally Posted by abstract
A pilot study was conducted under the auspices of the Coordinating Research Council, Inc. (CRC) to assess the potential effects of gasoline octane quality on acceleration performance, fuel economy and driveability in vehicles equipped with electronic spark control systems (knock sensors). Fourteen vehicles were tested by five participating laboratories on CRC un- leaded reference fuels of varying octane quality (78 to 104 RON). The test vehicles included nine naturally-aspirated and five turbocharged models. The results showed that acceleration performance was the parameter most sensitive to octane quality changes, particularly in the turbocharged models. No significant improvements in fuel economy were found with increasing octane. Driveability was not affected by fuel octane within the commercial fuel range, but three vehicles showed degraded driveability with sub-commercial octane fuels. Additional testing is planned within CRC to further quantify the effects of octane quality on acceleration performance in a wider variety of vehicles.

NOTE: 87 RON is probably something like 83AKI or 84 AKI (if you have a better RON-to-AKI conversion, let me know) - but the key point is that 87 RON is an impossibly low octane rating (for American pumps anyway).

In addition, read what BMW apparently has to say about putting 87 AKI fuel in our 91AKI engines:
- Running On Regular: Do Premium Vehicles Really Need Premium Gasoline?, From Stan Baldwin
Quote:
BMW explains using lower Octane gasoline

Straight from the BMW spokesperson, we get the final verdict regarding using 89 or 87 octane gas in our 91 preferred cars.
Running On Regular: Do Premium Vehicles Really Need Premium Gasoline?
From Stan Baldwin online

Long before gasoline rocketed through $4 a gallon many people were dismayed to see a significant percentage of their income disappearing into the tank of their car. Today, a wobbly economic outlook, increases in the cost of most other forms of energy, as well as the cost of life's staples, have prompted folks to look for every possible way to cut back on spending. "Can I save money by running my car on Regular?" "Will it hurt the engine?" my friends ask. More than one person driving a car the manufacturer has spec'd for Premium has told me "I use Regular and my car runs fine." Are there consequences of "down grading" your fuel? It is definitely a timely question, so we sent e-mail inquiries off to a half dozen manufacturers asking about their technology and their policy on the matter.

While waiting for their reply let's review some internal combustion engine characteristics. Fuel does not truly explode in a cylinder, at least it isn't supposed to. It burns smoothly, albeit very rapidly, across the cylinder. The octane rating is a measure of the propensity a given fuel has to burning, rather than exploding. Gasoline "exploding" in the cylinder is frequently called "detonation" or more colloquially, "knocking" or "pinging". These explosions, because they happen as the piston is rising during the compression stroke and try to shove the piston back down the bore, can do damage over time. In the case of severely stressed motors, such as in race cars, a few seconds of serious detonation can destroy the engine. Two of the mechanical considerations affecting how smoothly a fuel burns are compression and cylinder head configuration. Two variable considerations of great importance are the temperature in the cylinder and the ignition timing. Every manufacturer designs and builds their engines to operate most efficiently for the application intended with a gasoline of a particular octane rating.


Not all that long ago, before the advent of engine management systems, the result of tanking up a high compression vehicle with standard grade fuel was immediately obvious. Providing the stereo wasn't cranked up past 100 decibels, the pinging or knocking from the engine compartment let you know something was not right. Driving up a hill, towing a load or simply accelerating quickly produced an unnerving rattle from under the hood. It sounded very much like your carbureted V-8 had morphed into a diesel. Until the age of microprocessors enabled the creation of engine management systems, the consequence of a steady diet of low octane fuel could be fatal for a high performance engine.


General Motors, Honda, Toyota and BMW responded to our inquiry. Honda's public relations representative declined to comment on the issue. Toyota noted that essentially all their current models are designed to run on 87 octane. I asked about using 85 octane, available in some markets, and Bill Kwong of Toyota corporate PR told me they would run fine, with maybe only a slight 2-3 percent decline in horsepower and fuel mileage. But 85 octane is usually only offered in markets at altitude (i.e. Denver, Colorado) where the reduced oxygen doesn't allow an engine to reach full designed power in any event. If you drive a modern Toyota, the octane rating of your fuel isn't much of an issue. But what about a brand aimed squarely at the performance market? What about BMW?


Thomas Plucinsky, BMW Product and Technology Communications Manager told us all BMW engines are designed to run on 91 octane. All performance testing, including EPA emissions and fuel mileage, is done with 91 octane. However, though BMW is all about performance, their motors will run on 89 or 87 octane without damage. The knock sensors pull the ignition timing back and eliminate detonation. There will be a loss of power and a decrease in fuel mileage, but the size of the horsepower loss and the increase in fuel consumption depends upon many factors, such as ambient temperature, exact formulation of the fuel and driving technique, so BMW does not offer any estimates for operation on lower grade fuels. One not so obvious concern, Mr. Plucinsky noted, is the type and quality of additives the gasoline companies include in the fuel. Premium gasolines may have better additive packages which are more effective keeping fuel systems (particularly injectors) clean and working efficiently, than those in regular grade fuels or off-brand products. Using lower octane or off-brand fuel could be degrading the fuel system over time, setting you up for a repair bill down the line.


Dave Muscaro, Director of Engine Development/Calibration for GM power trains explained GM has "three flavors" of fuel specification for their offerings: Regular (87 octane) Recommended, Premium (91) Recommended, and Premium Required. Again, we are more concerned with the last two categories where regular could be substituted for the specified Premium. All the engines have a knock sensing ability that retards the spark when detonation occurs. For the premium recommended vehicles the spark advance will be pulled back enough to eliminate the detected knocking. The typical driver will not notice a performance decrease, except under load, and mileage will decline slightly. The engines intended for performance, such as the LS7 or the supercharged small block V-8, are Premium Required powertrains. The customers clearly were not primarily concerned with economy when they chose a performance vehicle and GM optimizes the engine management system to deliver the highest possible power output at all times. To this end the detonation control system does not retard the spark to the point required to prevent all knocking. It would seem a determined deranged drag racer could run Regular in his Corvette and, over time, he might manage to melt a piston or two.


If burning 87 octane in your car, when 91 octane is specified, will not harm the engine, and the performance degradation is not noticeable in typical driving, how much money can you save? The Energy Information Administration, U.S. Government Department of Energy, offers some figures for US gasoline retail prices (these are averages, all areas, all formulations). A year ago Regular was going for $2.982 a gallon and Premium was commanding $3.196 a gallon. The 21.4 cent difference delivered a 6.7 percent saving over Premium. This June 23, 2008, Regular extracted $4.079 from your wallet while Premium sucked up $4.312 for every gallon. The differential (23.3 cents) has grown slightly since 2007 but buying Regular is now only 5.4 percent cheaper than Premium. Since 5 percent is roughly the typical percentage of mileage decrease to be expected with the 87 octane fuel in a 91 octane engine, is there any savings at all?


Bottom Line: Most modern engines are fuel injected and controlled by sophisticated engine management systems which can rapidly and accurately compensate for lower octane fuel by retarding the ignition. Running these cars on 87 octane will not hurt them. However, the immediate savings at the pump may be wiped out by the subsequent drop in fuel mileage and performance
, not to mention the possibility of damage over time.
EDIT:
In addition, these may be useful:
Changes in Gasoline IV - The Auto Technician's Guide to Spark Ignition Engine Fuel Quality

Road & Track - Premium Fuel Futures - A primer on high-test gasoline: Is it for you?


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Last edited by bluebee; 02-14-2013 at 11:44 PM.
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  #109  
Old 02-16-2013, 02:19 PM
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540iman 540iman is offline
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I was traveling the exact same route every day and 95% of it was highway. I am anal about watching my gas mileage. I use my cruise control constantly to maximize gas mileage as it modulates the gas pedal the least. The whole deal with my 540 automatic is a wash so I use the premium. We get 93 octane here in Indiana. Premium is had for 30 cents over 87 octane regular which car runs "ok" on. So, 18 gallons times 30 cent savings is $5.40 a tank savings buying 87 octane.

My gas mileage suffers real close to 2.0 MPG using regular, so with an 18 gallon fill, The 2 miles per gallon equals 36 miles per tank. This is roughly 1.5 gallons of gas to get that 36 miles back. 1.5 gallons times $4 a gallon equals $6. Savings on buy side was $5.40 vs $6 so running premium costs nothing and is better for my 4.4L engine.
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  #110  
Old 11-18-2013, 12:13 PM
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bluebee bluebee is offline
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For the record, this gasoline grade question was asked today:
> E39 (1997 - 2003) > Gasoline grade question.
Quote:
Originally Posted by Hobel.587 View Post
I bought the 1999 528i. The previous owner maintained and serviced everything well. With records.

However. He has been putting low grade gasoline in it for 11 years, but says it's been fine.

I would like to start using premium. Will switching right now have any adverse effects? And is it worth it?

Thanks,

Jake
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  #111  
Old 11-18-2013, 08:59 PM
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bluebee bluebee is offline
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Just to be more complete, the cost differential question was discussed there also:
Quote:
Originally Posted by Burning2nd View Post
almost no one knows that it takes 2.5 to 3 full tanks of fuel for the trim to change...

so running 91 then 87 then 91 does nothing but confuse your car..

you want to test it for real?
you run it for a month or 6 month period... not tank by tank.

lol you kids are funny..
Quote:
Originally Posted by edjack View Post
It's easy in my 'hood: The per-gallon price spread between 87 and 91 octane is only 20 cents.
Quote:
Originally Posted by itsjustmb View Post
I can feel the difference in power when I use regular V premium. On 91 octane, the car just seems to run smoother and get going a lot faster. I also noticed the car liking 76 or Shell gasoline. Might be my mind trying to justify the Premium $4+ a gallon here in CA lol
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  #112  
Old 11-18-2013, 09:38 PM
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bluebee bluebee is offline
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BTW, did we ever figure out if there is an easy way to determine if the knock sensors are activating?

Quote:
Originally Posted by bluebee View Post
Yup. The AKI (which is the average of two different rather loose measurement methods), is a measure of how well the fuel "resists detonation" (under heat and pressure) as compared to a test mixture of 2,2,4-trimethylpentane (aka "iso octane") and normal hexane of the same ratio as the octane rating.

Higher AKI numbers match higher tri-methyl-pentane percentages, hence, higher octane rated fuels resist detonation better than lower octane rated fuels.

Hence, if your engine wasn't knocking to start with, then it's impossible to get any appreciably better performance or gas mileage (at least appreciably more than the error in your measurements) with either fuel, since nothing is, in effect, changing.

Now, IF (and this is the big if), if your engine was knocking, well then, going to a higher-octane rated fuel should noticeably change things, for the better. Of course, the ubiquitous presence of piezoelectric knock sensors makes that assessment difficult, in the rough.

I wonder ... is there any way for us to tell if the knock sensors have detecting knocking in, say, the past FTP?
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  #113  
Old 11-19-2013, 07:16 PM
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bluebee bluebee is offline
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This related post happened today so I bring it here for cross reference:
Quote:
Originally Posted by plmadding01e39 View Post
Actually my car costs more than $95.68. Where I am 91 octane is 23 cents more than 87 octane. I usually fill 16 gallons every other week. That works out to $3.68 more for 16 gallons of 91 octane. Filling up 26 times (every other week for a year) this adds up to $95.68. Really not much of a difference and most certainly not the cost of my car.
Quote:
We worked out many scenarios in the aforementioned thread:
- What is the cost differential between 87 & 91 octane AKI (1)

If you run that math for, oh, say your entire 50 years of driving time, that savings would only be $4,784. If your significant other did the same, the combined household savings would be $9,568.

So, in a lifetime, using the lower-octane-rated fuel, would save you about $10,000 for your household (assuming no loss in MPG - but see the detailed thread for those calculations).

You decide if that's much of a difference, or not.
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