The manual for the X3 says you can put 87 in it without doing any damage.

 

My 05's manual doesn't say that. It says minimum 91.

 

On occasion, I follow a half a tank of 93 with a fill up of 89 if I am low in the money clip. Most of the time, I just pay the extra $1.50 - $2.00 a tank. Never noticed any difference and have not specifically looked for any.

No big deal to me even if I am a Mechanical Engineer specializing in turbine engines. :angel:

Cheers

 

So really it's a question of economy and performance. Time to do some gas mileage studies! I did that once on another vehicle to determine the most ecnomical cruising speed.

At my job I specialize in rockets.

 

At my old job I used to get a lot of "red rockets" from my boss . I digress, in CA we (as far as i have been able to ascertain) only get 91 tops. We have the usual 87,89, and 91. This is probably mandated by the faceless bureaucrats in the omnipotent CARB which hold us all in thrall. We won't mention their MTBE screw ups in the recent past.:rofl: Anyway, given that CA probably has more BMWs running around (and dealers selling them) than most countries and we only get 91 octane, you can bet that BMW is going to "approve" 91 octane no matter what.:thumbup: I have used both 87 and 89 during the unlamented obscene gas price spike and actually found no problems in any way. The mileage seemed the same, the engine ran the same, and on hills I heard no pinging or knocking. If the price spikes again, I will go right back to the lower octane too.:bigpimp:

 

I think a lot of that has to do with the gasoline available in Europe. In most European countries, regular gasoline is 91 Octane unlike here where regular is 87 Octane. Since BMWs are tested on 91, it's only natural for them to guarantee their vehicles on what they have been tested upon, anything lower than that and you are on your own.

 

Actually, this post will probably restart the continuous discussion of the difference in Octane rating between Europe and the USA. :angel:

Cheers

 

The core of the issues for me (and a lot of other people) is the fuel requirement for our X3s and the desire to pay less at the pump. I don't mind paying for premium, but only if I must, and therein lies a gray area (which I will explain).

The manual says use at least 91 octane. Well, around here we have 87, 89, and 93. So your choices are either less or more. It's hard to argue that 93 is not the "best" choice, but I wonder if there are other choices that are actually better when factoring in cost.

I assume that using any gas above 91 provides negligable (or no) mechanical benefit to the car. One can argue (largely based on marketing efforts by gas companies) that the highest grade provides superior additives, but I have seen no evidence that, even if true, they will give any benefit - more economy or avoidance of engire repairs. As for additives, I'm going to leave that out of my analysis. Of course they make a difference, but the benefit, in my opinion, is largely based on the brand (i.e. Shell vs. generic) rather than grade.

For all I'm considering, here are the core issues: economy, avoidance of engine repair, and to a lesser degree performance. I don't care if a gas (or oil or whatever) does "wear" or otherwise degrade the engine as long as it doesn't lead to poorer economy, performance, or a quantifiable repair.

So here's where I'm going. I want to know if I can use 89 or a mixture of 89 and 93 (by filling half tanks of each or alternative grades at half take fillups) and achieve the same economy, performance, and engine life as using exclusively 93. Another option is to alternate full takes of 89 and 93.

Does anyone have any data (i.e. fuel economy comparision) related to use of different grades of gas?

Unanswered question: Is there any added benefit to using 93 octane versus 91?

Answered question: Highest grade has superior additives? No, Chevron, Conoco, Phillips 66, and 76 state that their additives package is the same for all octane. Shell says they have twice the minimum concentration of additives in regular and 5 times the minimum required concentration of additives in premium.

Answered question: Premium does result in better gas mileage of about 1 mph on the highway in a test that they published in 2005 using 1 model of car, not BMW. My own test year long test confirms this, but it was more like 0.75 mpg.

Answered question: How about mixing gas? It is a known fact that if you buy premium gas from a station that has a single nozzle, not 3 per island, then you will be getting some (1/3 gallon?) of regular if the last person bought regular. Someone who has a motorcycle and small gas tank asked this to a car column in the Wall Street Journal. So if you mix gas, buy premium first then regular and you will be getting all the premium you paid for.

I sometimes mix gas to get 91 octane. I carefully record the calculated octane in my tank. This makes me an inch from being admitted into a mental hospital.

 

... So here's where I'm going. I want to know if I can use 89 or a mixture of 89 and 93 (by filling half tanks of each or alternative grades at half take fillups) and achieve the same economy, performance, and engine life as using exclusively 93. Another option is to alternate full takes of 89 and 93.

My insightful analysis is:

- using 89 grade exclusively (or even 87) will have no demonstrable effect on engine life

- whether it will have a noticeable effect on performance may vary from person to person

- measured differences in performance/economy might be smaller than the margin of error

- savings with 89 grade for non-demanding urban driving may be worthwhile

- savings with 87 grade might be questionable because of lack of some key additive

- additive in some mid/premuim brands puports to prevent fuel gauge sensor corrosion

- doing half fills with 87 and 91 at the gas station is too inconvenient

- doing alternate fills with 87 and 91 is a cop out

Without getting into the differences between R.O.N. and A.K.I.,
it is worth pondering the fact that in many parts of Europe, their "regular" gas
is equivalent to our "mid-grade" at the very least.

No need to debate the reasons for that, but if you fold it into the reasoning, you may conclude:

- probably best to just suck it up and pay for 91 or 92

- but don't sweat it if you prefer to use 89 or even 87

And finally, as has been discussed recently:

- avoid running more than a few miles with the low fuel light on

- try to patronise well-used gas stations with newer-looking pumps

- don't fill much past the first auto. shut off

- always get a receipt, just in case unexpected problems arise after the fill up

 

...and for goodness sake, stay away from BP stations as they refuse to publish their fuel ingredients.

http://www.bimmerfest.com/forums/showthread.php?t=408759

 

European cars are designed to run on Eurograde gasoline. Octane spec is 95 RON/85 MON or 90 R&M/2. There is no 90 R&M/2 gasoline in the US, hence the 91 R&M/2 recommendation in the owners manual. Your BMW will get maximum performance and efficiency on 90 R&M/2 gasoline. The use of higher octane will do nothing. Conversely, the use of 87 R&M/2 gasoline will hurt nothing, the knock sensors present in every car retard the ignition timing as needed. You may notice a slight decrease in performance and efficiency, depending on your driving style.

The exception is the high performance models, which may have the ECU calibrated for 91 R&M/2 or even 93 R&M/2 premium. In these cases there will be wording in the owners manual to use 91 R&M/2 or 93 R&M/2, and only use lower octane in an emergency and to drive easily until the tank can be refilled with the proper octane. My Infinity G37S and now my Nissan GT-R have this type of language. Normal BMW's do not have this type of warning.

 

European cars are designed to run on Eurograde gasoline. Octane spec is 95 RON/85 MON or 90 R&M/2. There is no 90 R&M/2 gasoline in the US, hence the 91 R&M/2 recommendation in the owners manual. Your BMW will get maximum performance and efficiency on 90 R&M/2 gasoline. The use of higher octane will do nothing. .

That's why Saab recommends 90 octane gas even though nobody sells it in the U.S. You can mix 87 and 93 to get 90, though. Just half and half. :rofl: Don't be sloppy, measure it exactly :rofl:

 

91 or greater all the time.

I get 24.2 - 24.5 mpg consistently.

 

Winter vs Summer

Something I have noticed is that, for obvious reasons, my car runs much better when the outside air temps drop in the fall and winter. Your vehicle is able to breather more freely. The performance as judged by the seat factor is to me very noticeable. During the hot humid summer days, performance lags. Hence my habit of using regular during the cooler months and mid or performance grades (depending on the price at that time) in the summer months to regain some of the lost performance due to the hot humid air my car is breathing.

 

Something I have noticed is that, for obvious reasons, my car runs much better when the outside air temps drop in the fall and winter. Your vehicle is able to breather more freely. The performance as judged by the seat factor is to me very noticeable. During the hot humid summer days, performance lags. Hence my habit of using regular during the cooler months and mid or performance grades (depending on the price at that time) in the summer months to regain some of the lost performance due to the hot humid air my car is breathing.

Cold air + cold fuel = zoom-zoom :thumbup:

 

Air Density

The reason your engine performs better in cooler temperatures is due to the increased air density. This happens when temperatures drop. As a result your engine inhales more oxygen per "breath". I know this because I fly single-engine light aircraft and they also perform much better in the winter too!

A chemist may cite the ideal gas law to prove this: V=(nRT)/P, where V=volume.

In my X5, I do not see too much of a difference as I believe the computer adjusts the fuel-air mixture to compensate for the temperature or oxygen content. I do not know too much about how BMW controls these variables though. Just a guess. If you are seeing a large difference in performance due to temperature, you may have a problem with your temperature sensor. There may also be a change in MPG depending on temperatures as well, with your fuel-air mixture being too rich on hot days.

Just my $0.02