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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Mid grade vs. Premium gas



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      08-13-2007, 06:07 PM   #1
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Mid grade vs. Premium gas

I'm filling up my first tank of gas on my new 328i. The dealer said the vehicle will run on mid-grade gas. The service manual says you should run the car on premium. Has anyone had problems with mid-grade or done this before?
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      08-13-2007, 06:13 PM   #2
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the car will run on even on low grade gas (87). it's just that you won't get all the power and MPG as you should be if you use premium. There is a sensor there that determines what gas you put in and adjusts accordingly. I wouldn't put anything less than Premium in and stick with brand name gas
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      08-13-2007, 06:29 PM   #3
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the car will run on even on low grade gas (87). it's just that you won't get all the power and MPG as you should be if you use premium. There is a sensor there that determines what gas you put in and adjusts accordingly. I wouldn't put anything less than Premium in and stick with brand name gas
If I had a 328, I'd just use premium. But the lower MPG thing seems to be an urban legend that just wont go away. Octane rating has nothing to do with MPGs, it has to do with predetonation. The MPG thing is such a myth that there are people using super whose motors are designed for regular unleaded. Talk about burning money out the tailpipe.
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      08-13-2007, 07:06 PM   #4
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I had a 2004 X3 with the 3.0 and only used mid grade and have a 2007 X3 and only use mid grade. Never had a problem with either and really can't tell the difference with premium. I only put premium in my M3 and 335i.
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      08-13-2007, 07:20 PM   #5
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Originally Posted by John 070 View Post
If I had a 328, I'd just use premium. But the lower MPG thing seems to be an urban legend that just wont go away. Octane rating has nothing to do with MPGs, it has to do with predetonation. The MPG thing is such a myth that there are people using super whose motors are designed for regular unleaded. Talk about burning money out the tailpipe.
MPG will be worse if a car designed for 91 is run on lower octane. MPG will NOT improve if a car designed for 87 is run on 91.

So we have a BMW designed for 91 and put in 87. Assuming it really is 87 (note that the pump says “minimum”) detonation will probably occur, leading to the engine control unit retarding the timing. The car will then run OK, but the retarded timing will cost power and result in lower MPG.

I think the dealer’s advice to the OP was correct—the car will run on lower octane. And the manual is correct, it should have 91.
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      08-13-2007, 07:20 PM   #6
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If the car is a leased car I'd always run it on 87. Lots of my friends who have leased S-classes do that, saves money and who cares its not your car.
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      08-13-2007, 07:21 PM   #7
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If I had a 328, I'd just use premium. But the lower MPG thing seems to be an urban legend that just wont go away.
I know what you're saying... if a car does need premium it's a waste of money to buy it. But if a car calls for premium and you don't use it, you'll get the predetonation (knocking) problem which will probably hurt MPG. I bet that's what nhhiep was referring to.
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      08-13-2007, 07:21 PM   #8
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If I had a 328, I'd just use premium. But the lower MPG thing seems to be an urban legend that just wont go away. Octane rating has nothing to do with MPGs, it has to do with predetonation.
If your gas isn't detonating at the optimum time then the engine isn't running as efficiently as possible. If that's the case I don't see why it's illogical to conclude that MPG could/would suffer. Although MPG/performance does not correlate directly with the octane rating, ignoring the recommendations of the engineers who designed your engine can correlate directly with a decrease in MPG/performance.
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      08-13-2007, 07:22 PM   #9
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... saves money and who cares its not your car.
How much money are you actually saving? Maybe a couple bucks per fillup? It's not worth the decreased performance.
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      08-13-2007, 07:22 PM   #10
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I've run mine anywhere between 87 to 91 without noticing any difference, either performance or mpg. Then again my elevation is around 4000 to 8000 ft so AKI is not as critical.
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      08-13-2007, 07:23 PM   #11
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lol.... looks like several of us replied to john 070 at about the same time.
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      08-13-2007, 07:42 PM   #12
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fill in with premium. It's just 10 cents diff per gallons, $1.60 diff per tank.
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      08-13-2007, 07:45 PM   #13
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MPG will be worse if a car designed for 91 is run on lower octane. MPG will NOT improve if a car designed for 87 is run on 91.

So we have a BMW designed for 91 and put in 87. Assuming it really is 87 (note that the pump says “minimum”) detonation will probably occur, leading to the engine control unit retarding the timing. The car will then run OK, but the retarded timing will cost power and result in lower MPG.

I think the dealer’s advice to the OP was correct—the car will run on lower octane. And the manual is correct, it should have 91.
Wrong. Octane has nothing to do with what MPG the motor can yield. You're perpetuating erroneous information.
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      08-13-2007, 07:50 PM   #14
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Originally Posted by Zephyr15 View Post
If your gas isn't detonating at the optimum time then the engine isn't running as efficiently as possible. If that's the case I don't see why it's illogical to conclude that MPG could/would suffer. Although MPG/performance does not correlate directly with the octane rating, ignoring the recommendations of the engineers who designed your engine can correlate directly with a decrease in MPG/performance.
I've actually a 335 manual in my possession. You'll get yours when you get the car. When you read it you'll find you do need 89 minimum for the 335. But 89 will not yield lower mpg than 93. People in Cali. who can only get 91 for the most part do not get worse mpg than the rest of the country who use 93. As a matter of fact, 93 isn't even recommended--91 is. You may even be surprised at what the BMW manual says about "knocking sounds."

Most people should use premium. That's my opinion. That lower octane does not lessen the mpg is not my opinion, that's fact.
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      08-13-2007, 07:51 PM   #15
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Originally Posted by BMW335icDDS View Post
If the car is a leased car I'd always run it on 87. Lots of my friends who have leased S-classes do that, saves money and who cares its not your car.
but your going to feel the difference in the performance during those 3 years. If your going to buy a 50+ grand car and can't afford premium gas, then maybe you should consider getting a honda. Your willing to save 15-30 cents a gallon. really, how much are you saving? is it worth the under performance of your vehicle? why buy a vehicle that will perform if you will not use it to its most potential! i put 87 on my c-class last year by accident, and i felt the difference in the car! DON'T BE STINGY ON YOUR CAR!
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      08-13-2007, 07:51 PM   #16
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Wrong. Octane has nothing to do with what MPG the motor can yield. You're perpetuating erroneous information.
In that case, please clear up this public misperception by explaining the science and engineering involved in your own words or by citing a reputable source. I'm not being sarcastic, this is an open invitation for you to prove me and others wrong.
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      08-13-2007, 08:02 PM   #17
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Wrong. Octane has nothing to do with what MPG the motor can yield. You're perpetuating erroneous information.
So are you. What the heck is "predetonation"? Pick one: Pre-ignition or detonation. I'm not trying to be rude, but you don't know what you're talking about at all.

Also, octane can totally effect fuel economy. When pulling maps in Mitsubishi, Subaru, and Mazda ECUs while I've tuned them, all these cars actually jump to a different set of maps in the ECU when they sense detonation. This would be especially true if you use an octane that is lower than the car calls for. Not only do these extra safety maps retard timing, but they also enrichen fueling. Of course stoich for gasoline is not variable at 14.7:1, but fueling during varying load cycles will be richer when detonation is detected for protection. Hence, a reduction in fuel economy, unless you never change throttle input and remain at stoich 100% of the time. This would never happen, because acceleration demands work AKA more throttle input. Fueling is not a static value, its effected by load, RPM, temperature, and other things.

So you're the one perpetuating erroneous information.
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      08-13-2007, 08:08 PM   #18
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In that case, please clear up this public misperception by explaining the science and engineering involved in your own words or by citing a reputable source. I'm not being sarcastic, this is an open invitation for you to prove me and others wrong.
Chevron owns refineries and sells gasoline. Would they be a reputable source?

21. Will premium gasoline give better fuel economy than regular? Will one brand of gasoline give better mileage than another?
Gasolines with higher heating values give better fuel economy. Differences can exist, but they will be small compared to the benefits to be derived from the maintenance and driving tips in the above answer.

Traditionally, premium has had a slightly higher heating value than regular, and, thus, provided slightly better fuel economy. The difference — less than 1 percent better — is not large enough to offset premium's higher cost. The difference is likely to be less or nonexistent between grades of reformulated gasoline.

There can be differences in heating value between batches of gasoline from the same refinery or between brands of gasoline from different refineries because of compositional differences. The differences are small and there is no practical way for the consumer to identify the gasoline with a higher heating value.


http://www.chevron.com/products/prod...rgas/8_q-a/#21
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      08-13-2007, 08:10 PM   #19
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Chevron owns refineries and sells gasoline. Would they be a reputable source?

21. Will premium gasoline give better fuel economy than regular? Will one brand of gasoline give better mileage than another?
Gasolines with higher heating values give better fuel economy. Differences can exist, but they will be small compared to the benefits to be derived from the maintenance and driving tips in the above answer.

Traditionally, premium has had a slightly higher heating value than regular, and, thus, provided slightly better fuel economy. The difference — less than 1 percent better — is not large enough to offset premium's higher cost. The difference is likely to be less or nonexistent between grades of reformulated gasoline.

There can be differences in heating value between batches of gasoline from the same refinery or between brands of gasoline from different refineries because of compositional differences. The differences are small and there is no practical way for the consumer to identify the gasoline with a higher heating value.


http://www.chevron.com/products/prod...rgas/8_q-a/#21
That's for cars that call for 87 octane. Not cars that call for 91 and are mapped for it. You're going to have to better than that. I've seen dyno proof, you're cutting and pasting crap off the internet.
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      08-13-2007, 08:16 PM   #20
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That's for cars that call for 87 octane. Not cars that call for 91 and are mapped for it. You're going to have to better than that. I've seen dyno proof, you're cutting and pasting crap off the internet.
Don't quit your day job. Predetonation, AKI, reformulated gasoline don't ask what the ECU is calling for. They abide by physics and chemistry. btw, a dyno isn't primarily used to determine mpg. I wont offer you any proof on that, you'll have to do your own research.
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      08-13-2007, 08:17 PM   #21
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MPG will be worse if a car designed for 91 is run on lower octane. MPG will NOT improve if a car designed for 87 is run on 91.

So we have a BMW designed for 91 and put in 87. Assuming it really is 87 (note that the pump says “minimum”) detonation will probably occur, leading to the engine control unit retarding the timing. The car will then run OK, but the retarded timing will cost power and result in lower MPG.

I think the dealer’s advice to the OP was correct—the car will run on lower octane. And the manual is correct, it should have 91.
this is correct. i've read a couple studies throughout the years that document this. and yes, from my personal experience with cars that require 91, anything less will return lower fuel economy.
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      08-13-2007, 08:19 PM   #22
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I was just getting ready to say the same exact thing. Lower octane gas doesn't effect fuel mileage provided it doesn't detonate and go to a more conservative/ richer map. Once it does that you compound the problem with the car naturally running richer and using more throttle to compensate for the loss of power. This will most definitely effect fuel mileage.

If it doesn't go to a another map it doesn't make a difference though.
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