[335Newbie]

Hope this isn't a dumb question, but when I fuel up, my dash indicator says "x" miles to empty. Before each fill-up I zero the odometer thingy. I have however noticed this initial number ("x"), varies considerably at startup between 91 octane and 93 octane. I usually fill the tank with about 75 miles to empty. I am going to try to pin this down over the next several fill-ups.

[dmboone25]

The number you refer to as "x" usually varies on the kind of driving I have been doing--like, if I have been on the highway, the number is always higher. City driving--lower. Maybe that's the answer you are looking for.

[cazorp]

I'd say your figures should vary depending on average consumption since last fill, have you noticed any difference if you reset MPG before you check DTE?

[SoYank]

Isn't the range (X) determined by the average fuel usage over the past 18 miles? I seem to recall reading this somewhere, maybe in the manual.

That odometer "thingy", next to the odometer, is the trip meter and has nothing to do with the MPG or range calculation.

[HyperM3]

My car senses when Im hungry, aggitated, sad....sounds like you got a bum rap getting one that only knows the difference between octanes.

[Diesel]

yeah ... "x" is just calculated on how you have been driving.

[John 070]

With the subprime mess, I sometimes wonder if underwriters are just as arbitrary and seeing things that go bump in the night when they don't even exist. It's like a whole generation skipped HS math!

Here we go again with the different mpg with different octane fuel. That is a myth that's been busted many times using science. But the www seems to be able to keep it alive.

[cazorp]

Myth? Different octane means different energy values, which modern engines can adept for. With that said, a modern engine can use less fuel, on higher octane, providing the equivalent work.

[CokerRat]

Originally Posted by cazorp

Myth? Different octane means different energy values, which modern engines can adept for. With that said, a modern engine can use less fuel, on higher octane, providing the equivalent work.

Wrong. Octane is merely a measure of a fuel's propensity to precombust (ie. knock). It has nothing at all to do with energy value, and in fact the additives that are typically used to increase octane rating (eg. ETBE) have LESS energy per unit mass than straight-run gasoline does.

[Mattscott]

The car can tell. It measures speed and fuel consumption to come up with mpg. For example I filled up with 100 octane. My car is telling me I'm getting 6.0 MPG most of the time. (The lowest that it reads). My guess is that this is only because I am using more gas.

[m.rk77]

you are all correct but not about everything. Yes the MPG (X) varies greatly depending on your driving style, but the engine computers do detect the octane value of the gasoline and the engine will adapt to achieve best performance. Also the MPG will adjust accordingly.

BMW is not the only car maker with this technology. Most new cars have this...

With BMW this is part of the efficient dynamics technology...

[nicolak]

Originally Posted by CokerRat

Wrong. Octane is merely a measure of a fuel's propensity to precombust (ie. knock). It has nothing at all to do with energy value, and in fact the additives that are typically used to increase octane rating (eg. ETBE) have LESS energy per unit mass than straight-run gasoline does.

+1

I own an auto repair service, I try to explain this to my customers on a regular basis. It is especially difficult to convince the older generation why they must not use higher octane on engines designed for normal octane values. They wonder why they have difficulty starting during cold ambient temps, among other drive ability problems. Various late model American autos set adaptive fuel failure codes (o2 sensors, fuel trim, etc). I am usually made privy to this after spending much time diagnosing. It would be nice is someone could make a public service announcement.

[luckyD]

I had always used 93 until about 2 weeks ago, I tried 87 and it works perfect same gas mileage as with 93 no difference in power. I don't know if most people here are aware but in your manual for BMW 335 says that you can use 89 with out any problems. The difference between 89 and 87 octane's is so insignificant that it really makes no difference save your self some money and use 87 . The only way I would stick to 91 or 93 is if I had procede or some other engine tune that was requiring 93 octane gasoline

[Mattscott]

Thats not what the manual says at all. It says use premium unleaded gasoline only. If you have to in an emergency because premium is not available then 89 will have to do. You bought a $50000 car, are you really complaining about $3 extra a fill up for premium gas?

[am_ver]

Originally Posted by Mattscott

Thats not what the manual says at all. It says use premium unleaded gasoline only. If you have to in an emergency because premium is not available then 89 will have to do. You bought a $50000 car, are you really complaining about $3 extra a fill up for premium gas?

Its so much tempting though. I think it is more psychological than anything (with gas prices reaching levels that we haven't seen before)/

[m.rk77]

the engine sensors will adjust the engine so that you can use any octane gasoline. The reason why BMW does not want you to use low octane is because it generated more dirt in the engine which could mean more maintenance, which in turn would mean more expenses for BMW due to their free service.

So, use the cheapest gasoline but if they ask say you use the what is recommended in the manual because your warranty could be affected... Politics. Business.