What fuel grade?

[Franksauto]

Just wondering what fuel grade you run in your X5. Usually they say "Super Unleaded Only" on the gas gauge. My 06 4.8is says "Unleaded Fuel Only". I just filled it for the first time. I went ahead and filled with regular 87 octane unleaded. If thats a mistake I'll have to wait till she gets down some and refill with super.

[epdarks]

I don't think any BMWs ask for anything less than Premium fuel. You should really use the highest octane you can get, especially in the 4.8.

You may even get a check engine light with the 87 octane. You're not likely to do any serious damage, but the ECU will pull your timing so you won't make as much power.

I couldn't find anything from BMW, but here is a review from Motor Trend. Scroll down to 'recommended fuel', and you'll see it asks for Premium.

http://www.motortrend.com/roadtests/...s/viewall.html

[Franksauto]

Will do. Thanks.

[Naz24]

I always put in premium and laugh at people at the pump putting in 87

[TwinTurboGTR]

Yeah I agree. One time I cheaped out and put in 89 in. I usually go 93. 20 miles or so, SES light. So I checked the cap and all that stuff, nothing. Then refueled with 93, 20 miles, gone and hasn't come back. 91 is ok too. Sunoco used to have 87,89,91, and 94 which they called their Ultra, but I haven't seen it anymore. Now their Ultra is 93. Ultra is only 3 cents more than 91 and 8 cents more than Regular. It really doesnt add up to much.

[tomcat]

It says "Unleaded Gasoline Premium" inside the fuel door. I have read that saving money by getting lower grade gas is offset by decreased fuel economy.

Scott

[JCL]

Lots of misinformation in this thread.

Yes, BMW calls for 91 AKI (anti-knock index, not directly related to RON), but that is simply to cover the wide range of fuels actally sold in North America, of widely varying quality.

The correct fuel to use is the lowest AKI that does not result in a reduction in power or fuel efficiency, that being caused by the timing being retarded.

Anything over that is simply throwing money away. Those are the people I laugh at. Especially anyone who refers to higher AKI fuel as a 'treat' for their inanimate object.

If you measure your fuel economy from fill to fill (not relying on the on-board-computer or OBC), you will be able to determine if your mileage is worse on 89 or 87 instead of 91. If it isn't, no reason to use any higher AKI, unless it is a point of pride. Higher AKI does not have more energy, and your vehicle won't thank you.

Fuels are very different across North America. Think of the quality and actual AKI as being represented by a bell curve graph. BMW specifies a figure at the right side of that bell curve (91) to cover the most vehicles. Some areas will actually require all of that specification. Other areas with good quality fuel are fine down to what is sold as 87 or 89, and you have to test it to determine your local fuel quality.

With my E53, the best fuel economy I was able to get was on 89, so there was no reason to use 91. I tried 87, and used it occasionally, but I sometimes could tell that engine responsiveness wasn't the same, so I usually stayed with 89.

If you use 91 in the winter and have hard starting, your dealer will likely tell you to go to 89, as it can improve cold starts. Conversely, in summer, the AKI becomes more important due to higher ambients.

You will not get check engine lights just due to AKI rating. The engine runs just fine down to 87. There is no risk of damage. You may not get as much power, but that isn't guaranteed, as it depends on the actual AKI and the engine condition, not on what it says on the gas station pump. You can get check engine lights due to other fuel issues (water, ethanol %) but not AKI. Those problems sometimes get wrongly blamed on AKI.

The biggest fuel quality issue these days is ethanol %. That is more critical than the AKI. I buy 94 sometimes just because it doesn't have any ethanol, and the 91 has up to 5%. I can cover the price difference in the 94 due to improved mileage resulting from having no ethanol, and the 94 rating is irrelevant.

If you do use a lower AKI, with no difference in performance, then you are providing the right fuel to your engine. Don't expect to save much money, as the difference is very small relative to the price of the vehicle and your annual fuel bill. But that doesn't mean that you should throw money away on an AKI rating that your engine doesn't need. The fuel companies have sufficient profit without you providing more.

Edit: I couldn't remember the AKI degradation due to not having fresh fuel when ethanol is at 10% (typical), so I looked it up. After 100 days, or earlier if there is any moisture absorbtion, deduct 3-4 points of AKI. Thank the corn lobby for the nonsense that is ethanol in our fuel.

[TwinTurboGTR]

Uh huh. I thought the fuel/SES light was a little weird, just coincidence. Most of the time its because the fuel cap isn't secured properly. I mean 3 years ago, around here in Jersey, you rarely saw (Contains up to 10% Ethanol), but now, it is every where. Up until last year, I started filling up on the GSP Sunoco's because they did not have Ethanol, but now they do. 91 is difficult to find around here. Usually only Getty stations that are older carry it, but they are closing down one by one. So normally it is 87,89,93.

I should really read into the AKI and get schooled on it. But like you said, if there is only a nickel difference between 89 and 93, it doesn't matter??? I mean there was a time I ran 87 and the performance was light., sounded like the motor was sluggish, but again, might have just been me. So normally I just put in 93 and wait for a window reg to fail. lol

[SlickGT1]

I cannot find Ethanol free fuel at all. Nothing in my area, or surrounding areas. I call this bullshit.

[motordavid]

What JCL wrote, imo, (for the umptyseventh time)...

It's the weekly 'what grade/brand of gas should I use' post.

Most of the responses, across the pages of threads, are anecdotal.
My anecdotes:
-the best tank I ever got on the X, ~570 miles, was on 87 regular on a use up the tank in less than one day trip, with coolish temps, no A/C, etc.
-the best tank/mpg I ever got on the Vette was on our Road Trip last summer, in Montana. High elevation, ok temps, some A/C, hauling azz, on some no name 91.

As noted, the vagaries of every 'brand' of gas, the variance of posted octane, the % of ethanol, etc., all contribute to the chase. Do some 'Net reading on 'gas quality' and how the bulk delivery trucks, via the tank farms 'work', and it will make one go Hmmmm.
GL, mD