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Discussion Starter #1
Hi all!

New Bimmer owner and very excited about it!

2006 330Xi - 115k miles

My question is regarding gasoline. I understand that it is recommended to use 91+. How important is that? Have any of you more experienced owners had any issues using 87 or 89? Thanks a lot in advance!
 

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Buy gas from a dealer listed in www.toptiergas.com. Why? BMW and other manufacturers got together and determined how well gas needs to clean the injectors and the back side of the valves. 91 octane is recommended, but you can use 89 octane without issue. The engine computer (ECU) determines when to retard the ignition. As a result you'll experience some reduction in performance in some conditions when using 89 octane.
 

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Your 330i is a non turbo and will run fine on 87 octane, although peak power and fuel mileage might suffer slightly.

My 328i is tuned for 91 octane, but since 87 is acceptable, I generally alternate tanks of 93 & 87. I've been buying primarily from local off brand stations (heavier traffic = fresher gas) for 5 different Bimmers for 20 years with absolutely no problems, other than a heavier wallet.

Tom
 

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Discussion Starter #5
Thanks all. I appreciate the feedback. Knowing it's ok, I'm going to run a tank on 87 and then one on 93. I use a fuel tracker app so I'll see the difference in mpgs between the two and see the loss/gain of mpgs vs the price difference and decide which to use after that.

Thanks again
 

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My criteria, in order of importance, is:

1. Use gas, never diesel, if your car is a gasoline car. :rofl:
2. Use at least the minimum octane according to the owners manual. For some BMW's it's 87, 89 for mine, 91 for others.
3. Buy gas from a station that seems reliable in terms of gas not being too old, no water in the tanks (if you can guess)
4. Buy gas of a reputable brand. AAA recently tested gas and wrote that Top Tier brands did have less engine deposits. On the other hand, Top Tier gas is required to have 8-10% ethanol but it is increasingly very hard to find gas without ethanol.
5. Buy premium gas, 91-93 octane. You will get better gas mileage but maybe 0.2-1 mpg at most. The EPA tested cars and found that to be true but politically incorrect. Uncertain is whether 93 offers any advantage to 91. If not and you live in an area with 93, you could be economical and buy 3/4 93 and 1/4 87, which comes out to be roughly 91.

I don't alternate octane because when you put 87 in, it may knock until the sensor detunes the car. I just use 92, which is close to 91. There is no 93 here. There is 94 in Canada, at a much higher price and a quarter tank of gas away so not worth it.
 

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Discussion Starter #7
1. Duh?
2. My cap says 91. Book says 87.
3. I use a Sheetz that is right off a major highway. They get delivered to daily.
4. I'll have to look.
5. My current test will determine if the 0.2-1 mgp gain outweighs the cost difference. I'm not expecting it to.
5a. Good point. I'll stick with one or the other.

Thanks for the input!
 

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Discussion Starter #8
Finally have enough data(fill-ups) to provide this data.

3 tanks of 89:
Average 293 miles
Average 13.09 gallons
Average 22.38mpg

3 tanks of 93:
Average 361 miles
Average 14.515 gallons
Average 24.87mpg

87:
300 miles ÷ 22.38mpg = 13.4g
13.4g × $1.94 = $25.966

93:
300 miles ÷ 24.87mpg = 12.06g
12.06g × $2.44 = $29.67

Conclusion
93 would cost me approximately $4 more than 89 per 300 miles.

Being that this cost difference is so miniscule, do you think there is a benefit to engine component health in using 93?
 

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I would use the highest the factory recommends, I find this information on the gas cap. Your vehicle will detect whether it is 87 or 91 or whatever octane and adjust accordingly.

Personally since your vehicle says 91 on the cap I would think 93 octane would be a waste. I think it would be a waste of a BMW if you used 87 octane.
 

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Very well if 91 is not an option I would highly recommend 93. The car is designed to use 91 so 93 won't hurt but under 91 is not a good idea. I could talk your ear off about long term problems but it is all hypothetical. Basically if you run inferior gasoline you might need a long list of things like new spark plugs and that is a couple hundred dollar job to do yourself with the proper parts. BMW's are actually fairly environmentally friendly and using the proper gasoline contributes to BMW's having not a drastic environmental footprint.

Using 91 or 93 octane on a car that has 87 on the gas cap is an absolute waste of money.

P.S. I am from Canada, all my BMW's have had 91+ on gas cap. Regulations about measuring gas may be different in the USA and cars may be different specs. In Ontario we get 87,89,91 everywhere and maybe 94 at limited locations.
 

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02/2012 X5 35d M57Y CPO 100K miles NOKIAN WR G3 20K miles
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One of the pros of Variable Valve Lift is reduced dependence on octane.
 

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Finally have enough data(fill-ups) to provide this data.

3 tanks of 89:
Average 293 miles
Average 13.09 gallons
Average 22.38mpg

3 tanks of 93:
Average 361 miles
Average 14.515 gallons
Average 24.87mpg

87:
300 miles ÷ 22.38mpg = 13.4g
13.4g × $1.94 = $25.966

93:
300 miles ÷ 24.87mpg = 12.06g
12.06g × $2.44 = $29.67

Conclusion
93 would cost me approximately $4 more than 89 per 300 miles.

Being that this cost difference is so miniscule, do you think there is a benefit to engine component health in using 93?
Modern cars de-tune themselves when inaudible pinging is detected. So, by running your car with sub-standard gas, you're forcing the car to de-tune. That could increase the carbon build-up in the combustion chamber over the long term. Severe pinging could actually damage the engine, but you'd hear it first.

You can make your own 91 AKI by mixing 1/2 89 AKI and 1/2 93 AKI, or 1/3 87 AKI and 2/3 93 AKI. The 87-93 AKI blend is usually the cheaper combination. They don't make 89 AKI gasoline. It's blended at the tank farm from 87 AKI and 93 AKI. The AKI is a weighted average of the blends. By tracking your MPG with the on-board computer (resetting the MPG when you fill up) you can accurately predict how much gas you will need before filling up the car.

Ethanol only has 2/3 the energy (latent heat of combustion) of pure gasoline. So, E10 (10% ethanol) only has about 97% the energy of pure gasoline, resulting in only 97% the MPG of pure gasoline. E10 is mandatory in the US, supposedly to reduce emissions during cold start-up and with older cars without O2 sensors, and to reduce our dependence on foreign oil. But, it's really just to pay back the "corn lobby" for their generous campaign contributions. The corn lobby is trying to up the mix to 15%.

Field testing (like you've done) has a lot of unknown variables (AC use, traffic, tire pressure, etc., etc., etc.). But, if you got the same results with 91 and 93, then paying for 93 would be a waste of money and not improve performance significantly. Use 93 AKI on track days, though.

Oh, an vacuum out your floor. That sand there is driving me nuts. I can't look it at.
 

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finally have enough data(fill-ups) to provide this data.

3 tanks of 89:
Average 293 miles
average 13.09 gallons
average 22.38mpg

3 tanks of 93:
Average 361 miles
average 14.515 gallons
average 24.87mpg

87:
300 miles ÷ 22.38mpg = 13.4g
13.4g × $1.94 = $25.966

93:
300 miles ÷ 24.87mpg = 12.06g
12.06g × $2.44 = $29.67

conclusion
93 would cost me approximately $4 more than 89 per 300 miles.

Being that this cost difference is so miniscule, do you think there is a benefit to engine component health in using 93?
+1
 

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Discussion Starter #15
Autoputzer,
Thanks for the informative reply.
Also, it's not "sand" but where the carpet has worn. The car was at the shop and just detailed when I took the pictures. Feel free to buy me a new carpet if it bothers you that much! :)
 

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Autoputzer,
Thanks for the informative reply.
Also, it's not "sand" but where the carpet has worn. The car was at the shop and just detailed when I took the pictures. Feel free to buy me a new carpet if it bothers you that much! :)
I'll just resist the urge to click on the picture.

BMW carpet and floor mats are not known for durability. I bought two spare sets of floor mats when I bought my 535i. I alternate using the back mats to protect the driver's floor mat. You got me all freaked out now, though. I'm going to now have to watch my carpet, not just the mats.
 

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Discussion Starter #17
Oh I completely agree. Granted, the car is 10 years old, but I still don't interested so much wear UNDER the floor mat.

I've since picked up some custom sized floor mats for added protection.
 

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BMW carpet and floor mats are not known for durability. .
I agree. I noticed a tiny amount wear on the thin floor mats after just a few days of use during European delivery so I immediately replaced the mats with aftermarket carpet mats in the summer and rubber mats in the winter.

You can make your own 91 AKI by mixing 1/2 89 AKI and 1/2 93 AKI, or 1/3 87 AKI and 2/3 93 AKI. The 87-93 AKI blend is usually the cheaper combination. They don't make 89 AKI gasoline. It's blended at the tank farm from 87 AKI and 93 AKI. The AKI is a weighted average of the blends. By tracking your MPG with the on-board computer (resetting the MPG when you fill up) you can accurately predict how much gas you will need before filling up the car.
A long unanswered question is whether US BMW's are tuned so that the optimal octane is 91 or whether that is a politically motivated statement to make owners happy in areas that 91 is the highest octane sold.

If 91 is the optimal octane, I was thinking of pumping 2 gallons of 87 for each tankful which would lower the octane to about 91. If you have 92 octane, then it might be 4-5 gallons of 87 depending on how empty the tank was.
 

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AKI (final) = [ AKI (old gas) x gallons (old gas) + AKI (new gas1) x gallons (new gas 1) + AKI (new gas 2) x gallons (new gas 2) ] / [ gallons (old gas) + gallons (new gas 1) + gallons (new gas 2) ]

If your goal is to repeat the AKI of the old gas, e.g. 91 AKI, the (old gas) components drop out of the equation. Also, the less old gas still in the tank, the less it affects the final AKI after fill-up. I wait until I only have about 1.5 gallons in a 18.5 gallon tank before refilling. I calculate how many gallons I need (trip odometer miles since the last fill-up / MPG since the last fill-up), divide by three, and put that many gallons of 87 AKI in. Then, I finish up with 93 AKI.

Where I live, 93 AKI is $0.55/gallon more than 87 AKI. Between my two cars, both requiring 91 AKI, I burn about two gallons / day. By blending to make 91 AKI, I save about $135/year.

Since 91 AKI is the highest AKI readily available in California and a lot of high-altitude areas, BMW tunes their "50 state" cars to get by on it. I generally drive my 535i gently to get better fuel economy (one reason I didn't get an M5), so 93 AKI likely wouldn't benefit me. I flog my other car on 91 AKI and never hear pinging. I used to very occasionally hear pinging on my E46 M3 when the engine was lugging down (e.g. going up a grade at 55 MPH in 6th gear, in the summer, with the AC on). If I'd downshift, it'd go away.

Frau Putzer's 130k mile Honda Accord is just now showing wear on the driver's floor mat. My Cobalt's wore all the way through before I even noticed. I always buy at least one set of spare OEM mats when I buy a new car. If I don't use them, the next owner gladly buys them for what I paid for them. I might lose ten years of interest, but it pays for peace of mind.
 
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