89 Octane gas

Are there any negative side effects to using 89 Oct gas rather than the "required" 93 octane? How about 91 octane? So far I haven't heard any
pinging or knocking and the car seems to have the same pickup. I have a 2002 325i and a 2006 X3. Thanks
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Neither of those vehicles requires 93 octane; BMW recommends 91 octane.
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The knock sensors will detect pre-detonation and the computer will retard the timing to prevent it. You will get less power, and somewhat less mileage.
FloydR
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I use 89 in my 3 Series cars, a '94 and an '00.

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Gilbert Linder wrote:

How much of a cheapskate are you?
Run it on the proper stuff or buy a Nissan, fer christs sake.
Don't even start on fuel prices, how much is it for 93 octane? $4.55 per US gallon? I'm running an old '89 325i in the UK and feeding it proper fuel even though it's costing me $8.99 per US gallon.
Your two cars are worth a lot more than my old E30, so why are you even thinking of running them on cheap fuel? If you can't afford to fuel them properly, sell them. You may as well. Running a good car on rubbish fuel is like ordering a filet mignon in the finest restaraunt and then drowning it in cheap burger relish.
--
Pete M - OMF#9

BMW 325i SE Touring
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http://www.nextautos.com/running-on-regular-do-premium-vehicles-really-need-premium-gasoline 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?
This does not take into account possible future engine damage: 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.
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http://www.nextautos.com/running-on-regular-do-premium-vehicles-really-need-premium-gasoline
That's all well and good, but the OP asked about using 89 instead of 93, where there is an actual requiremnt of 91.
Bottom line, he can use 89 if he wants, but his cost per mile will remain pretty much the same. 89 costs less but delivers fewer mpg. Not a lot fewer, just enough fewer that the cost per mile will remain pretty much the same. 89 will possibly produce a lower cost per mile, _maybe_. I use 89 instead of 91 and find that it saves me about $1.00 on a tank full of gas. It ain't much, but it's a buck. I bothered a few times to calculate the cost per mile of mid-grade and of premium fuel, and with the cost per gallon difference of a dime, I found that the cost per mile was nearly identical, with the 89 octane gas getting a slight edge. I have to run the test again to verify my earlier findings, but I recall the savings to be about $1.00 on a tank. The cost per mile to drive was not perfectly offset, and the small margin went to the lower grade fuel.
Since I'm dollar-driven, I go for the lower grade and accept the cost as being less performance.
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My post addressed issues of using the lower octane gas when a higher requirement was specified.

As per my post.
Not a lot fewer,

App. .4% according to my post.
I use 89 instead of

You have to be mighty cheap to go with the lower grade, save approximately .4% in fuel costs while increasing the chances of engine damage in the future as you enjoy lower performance.
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There is no danger of damage by using 89 instead of 91.
The cost differential is insignificant too, except that 0.4% is a growing number as the price of gas goes up. Granted, the savings does not cover my beer tab at dinner with my wife, I have found no reason to not use 89 instead of 91.
My Jeep has an aftermarket fuel injection system. And when I installed it, the fuel requirement went from Regular (87) to Premium (91). It does not tolerate 87 at all, and balks at 89, so I have to use 91 to avoid engine damage. I know about the potential for big trouble resulting from using the wrong fuel, but my BMW is happy to run 89.
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I guess you didn't read my post.
"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."

Gas going up has nothing to do with it. It is the price ratio of 89 octane to 91 octane. In my area that ratio is 4.33/4.53 or .95. According to the department of energy (see my earlier post please) using regular gas will result in a mpg reduction of 5%. So essentially buying regular gas will result in a savings of 4.5% at the pump but will result in a 5% reduction in mileage. All the mile increasing the chance of a mechanical failure down the line.
Sounds like a deal to me!!!!!
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Actually, a decreasing number. When gas was under $2, ($1.799, 1.899 and 1.999 say) there was a 10% savings going to 87 from 91/93, 5% with 89. Now it's $4, $4.15 and $4.30 or thereabouts? You do the math.
I've been unable to find anything other than anecdotal information regarding power/mileage losses with the lower octane fuels. For most of us, it would be almost impossible to create an experiment that would be controlled enough to offer empirical data that would compare the fuel strategy costs accurately.
If you're pinching pennies to operate your Bimmer, there are ways that are equally or more effective than doing it at the pump.
R / John
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And if you get around to the north side of the beltway, there are a few suburban MD stations now pricing at 3.909, 3.979 and 3.999 for 87, 89 and 93 respectively - although their usual is a 10 cent differential between grades.

For their R1200RT motorcycles BMW actually publishes a spec of 110 hp using 93 octane and 101 hp using 87.

Driving technique, for one.
Tom K.
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Check the Dinan site: http://www.dinancars.com/bmw/technial-info/dynamometer-testing-and-the-modern-bmw-engine
" The E46 M3 is an excellent example of an engine that is sensitive to octane. It has a very high volumetric efficiency as well as a very high static compression ratio of 11.5 - 1. The engine being tested was a stock M3 engine. It was first warmed up and stabilized using the method described previously for the M5, running 91-octane fuel. As you can see in Figure 22, where the engine was warmed up and the previously discussed testing procedures applied, the stock M3 produced 280 hp (Figure 22- violet line). We then replaced the 91-octane fuel with 93 (available in most parts of the country). The M3's computer was so quick to determine that the fuel had been improved that it only took four dyno runs for the timing to adapt to the increased octane and raise the power up to 291 hp (Figure 22 - light blue and yellow lines). A gain of 11 hp with just 2 points of octane. "
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It turns out that my car actually has 89 as the spec, not 91. I feed it 89 because that's what it wants. I was thinking I fed it 89 because it tolerated it.
But you guys are all correct, I'm saving at most $1.50 per tank on the fill up, and could actually have a higher cost per mile that can eat the buck and a half over 300-ish miles. (Assuming a price difference of a dime between the cost of one grade and the next higher grade, and a fill up of 15 gallons.)
I just did some math, and was shocked.
Using my earlier assumption of a dime difference in the price of one grade and the next higher grade, I did some calculations.
If the higher grade costs $4.00, then the lower grade will cost $3.90. If the car takes 15 gallons to fill, and goes 300 miles, then the full tank costs $60 and $58.50, respectively.
If the higher price fuel gives a range of only 308 miles as opposed to 300 miles, the extra cost will pay for itself.
Using the figures I pulled out of my ass, the $4.00 gas costs 20 cents per mile, but the lower grade for the same distance only costs 19.5 cents per mile. 15 gallons @ 4.00 costs $60, @ $3.90 it costs $58.50. If I divide 5850 by 300, I get 19.50 (or, $0.1950) per mile. In order to get the same cost per mile for the more costly fill up, I only need to go 308 miles, that's only 20.5 MPG. ONE HALF MILE PER GALLON is all I need to recover the added dime per gallon for the higher grade.
In other words, if the proper grade gives more than one-half MPG better mileage, it pays for itself.
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Jeff Strickland wrote:

You're also an idiot who think that the Earth is like 10,000 years old, Jeffy.
Sheesh. The cost difference ain't enough to worry about.
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I just want to say that I have run my E28 on sub-85 octane Mexican gas, and while it retarded the spark like you wouldn't believe and had a tiny fraction of the normal acceleration, it ran smoothly and did not ping. I was impressed as hell... it's a pretty spectacular fuel injection system, especially considering how little compute power they had to work with inside that little 8-bit ECU. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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