[IM2C]

Tony, you seem like a good guy/dad. You've been a forum member for 4 years with 2k+ posts.

When you op with "I bought my son a brand new BMW and he want's to save a few bucks on gas", you will get a mixed bag of replies.

What seems like a nasty reply, might just be a joke. You don't own the forum, you're just a blip on the screen. Relax.

Cheers.

[SergioK]

Plan accordingly...

Every single BMW I've owned since the E36 has this neat thing where the ECU will 'learn' and 'adapt' to the fuel you use and, more importantly, what your right foot does. So, if you plan on taking your car to the track, use premium (sometimes I mix in some 100octane in there a well to get it up to 93-95 octane) and the engine will respond accordingly. It does so because modern BMWs have knock sensors that measure knock counts. The higher the knock count, the less performance and the ECU adjust accordingly. Less knock counts, the ECU kicks in to 'high gear'. It basically knows what fuel you are feeding the engine.

Your cousin that drives very modestly... she probably doesn't even push the engine past 3k rpm (which is a shame) but it also means very little stress on the engine which also means the engine probably spends most of its time putt putting along.

I, on the other hand, make my car's engine spend some quality time past 5000rpm on a somewhat regular basis so no, I do not ignore the fact that the engine wants/needs premium fuel when pushed.

[Elk]

Originally Posted by Agamemnon

The car is turbocharged, has direct injection, runs a high compression ratio, etc - therefore high grade fuel is a must

There are plenty of high compression turbo engines which can run 87 octane and the manuals for these cars indicate it is fine to do so. There is no simple bright-line rule to apply.

The OP's question is reasonable. BMW recommends 91 AKI, but also states 89 AKI minimum. I can appreciate his wanting to know specifically if anyone has run 89 AKI for an extended time to verify continued running of such fuel is acceptable.

[Agamemnon]

Fair enough.

[tony20009]

Originally Posted by SergioK

Plan accordingly...

Every single BMW I've owned since the E36 has this neat thing where the ECU will 'learn' and 'adapt' to the fuel you use and, more importantly, what your right foot does. So, if you plan on taking your car to the track, use premium (sometimes I mix in some 100octane in there a well to get it up to 93-95 octane) and the engine will respond accordingly. It does so because modern BMWs have knock sensors that measure knock counts. The higher the knock count, the less performance and the ECU adjust accordingly. Less knock counts, the ECU kicks in to 'high gear'. It basically knows what fuel you are feeding the engine.

Your cousin that drives very modestly... she probably doesn't even push the engine past 3k rpm (which is a shame) but it also means very little stress on the engine which also means the engine probably spends most of its time putt putting along...

I didn't know the engines "learn," but that's nice to know. TY.

Re: my cousin, yes, it is a shame. She was a Katrina sufferer and even three years after the fact, she was still going round and round with the insurance company about whether the rain/wind or the flooding destroyed her home. (Go figure....)

I bought her car too because the jalopy she'd bought after the storm just gave out, and she wasn't yet back on her feet really. I felt giving her a "special" car might lift her spirits and put her in a new frame of mind and because I know something about BMWs and I know little about other brands besides Honda and hadn't the time to spend evaluating them.

She's doing fine now that she's moved to the DC area (and out of my house which is good for her and me....) and found a job that pays nearly $100K/year, but had I known she's so tame behind the wheel (she was only 35 then, so I thought she was a bit more assertive behind the wheel....), I'd have just bought her an Accord instead. That said, the 328 I gave her is quite the stripper -- nav, sunroof and heated seats -- so it wasn't really all that much more dear than an Accord.

When it's all said and done, I'm just happy that I've been blessed so as to be able to provide for the folks about whom I care. All I can do is try to do right by them and seek always to give them the best I have to offer.

[1bad335]

[QUOTE=Elk;14204837]There are plenty of high compression turbo engines which can run 87 octane and the manuals for these cars indicate it is fine to do so. There is no simple bright-line rule to apply.

The OP's question is reasonable. BMW recommends 91 AKI, but also states 89 AKI minimum. I can appreciate his wanting to know specifically if anyone has run 89 AKI for an extended time to verify continued running of such fuel is acceptable.[/QUOT

I agree ^^

Ran 89 in my e90 for years and 10's of thousands of miles without a single negative affect. As for this car 89 is more than fine. My mpg is perfect. Just recorded 33.1 mpg on a 300 mile trip with eco pro. On a question like this you will get a lot of different answers. In the end you should do what works for you. The car will tell you if it does not like the fuel you're running. For me it is less about cost and more about why run what I don't need. I have actually run Sunoco 93 for an extended period of time to see if there was a difference and I can say, from my experience I saw and felt absolutely no difference. The owner's manual states clearly that 89 is acceptable for this car. I would not run 87 because I just feel that it is a little to low for this particular type of engine. IMHO, buying a quality fuel is what matters most.

[tony20009]

Originally Posted by 1bad335

...
Ran 89 in my e90 for years and 10's of thousands of miles without a single negative affect. As for this car 89 is more than fine. My mpg is perfect. Just recorded 33.1 mpg on a 300 mile trip with eco pro. On a question like this you will get a lot of different answers. ... I have actually run Sunoco 93 for an extended period of time to see if there was a difference and I can say, from my experience I saw and felt absolutely no difference...

TY for sharing your observations. I'll pass them along to my kid.

I assume you drive about as I would expect most folks here do: pushing the car a bit periodically, but most of the time just like other folks on the road, albeit accelerating a bit faster than most and cruising along on the highway a bit faster than the majority of other drivers. Yes?

[1bad335]

Originally Posted by tony20009

TY for sharing your observations. I'll pass them along to my kid.

I assume you drive about as I would expect most folks here do: pushing the car a bit periodically, but most of the time just like other folks on the road, albeit accelerating a bit faster than most and cruising along on the highway a bit faster than the majority of other drivers. Yes?

Exactly on the money. Best of luck to your son with the new ride.

[Steve33]

Originally Posted by tony20009

TY all who replied. Perhaps I need to clarify.

My son and I have both read the owner's manual. It says" BMW "recommends" 91 octane as the standard fuel and 89 octane as the minimum octane fuel. It also says that using fuel rated below 89 octane may impair performance.

So what I want to know if if anyone has OBSERVED a performance reduction and if so, under what circumstances?
- What octane fuel did you use?
- How long did you use it?
- What performance reduction did you OBSERVE?
- If it's relevant, what type of driving were you doing when you OBSERVED the performance reduction? (e.g., city driving where you floor the gas from stop light to stop light; highway cruising at some speed; driving like 90% of the population does around the 'burbs, hauling ass around remote, twisty rural roads as though you were on a race track; on a track, etc.)

Our motors don't run a high enough compression to NEED 91, that's why they have a minimum listed as 89. In Texas 93 is available some places, and I won't even put that in because running anything higher than a motor is designed for can actually decrease performance/mileage.

Since you only want observations (which are objective so really it's an opinion), I've experienced this with a Maserati, a F10 535, and 3 SUVs (Yukon 5.3L, Yukon Denali 6.2L, and a 5.3L Chevy Tahoe) while towing. In my opinion (Note: these are observatory opinions) I can't tell a difference running the next bump up or down in fuel octane performance wise, and there was never a noticeable difference in mileage. Anyone running anything remotely close to stock probably won't be able to tell (Close to stock = mppk, mpe, etc).

If you want to experience it, have your kid/wife fill your tank with one octane and don't have them tell you which one it was. Have them go back to the SAME STATION, and repeat with the other. You can get your own observations and won't have to rely on us and our opinions.

[B///MWGuy]

Hello. I would like to share my experience as you asked. Well, it's actually about my parent's car. My parents are quite conservative people (though they have two BMWs..I know..but they are conservative in other things). I have always told them to use the premium gas, but they never listened to me until recently. They once leased 2010 528i and had it for 3 years or so. They always put the lowest quality gas (I think it was like 85?--They live in SoCal). However, they never had any problem. I once pushed the car too, but it ran okay--no problem at all. Now, they have 2012 740Li and they also put 85 for few months until I really convinced them to put premium. 740Li has turbo charged engine. So it should be similar to your son's car. There is no problem so far, but my parents are pleased to see gained MPG.

And my thoughts:
I believe, having low mpg due to low grade gas cost you in the end as much as you would spend 2-3 more dollar for premium gas. One more benefit for premium gas is peace in mind. So premium gas > low grade gas.

Although this is very very rough estimate, I tried to think in the following way. Lets say Premium gas price is $4, while lowest gas is $3.80. 328 est mpg is 23city-33hwy. Lets just average that to be 26mpg. If fueling low grade gas subtracts 2 average mpg, then the average mpg would be 24mpg. Now, 328 has 15.8 gallon tank. Lets now calculate this. Premium fuel scenario: 15.8 x 26 = 410mi range in a full tank. Low grade fuel scenario: 15.8 x 24 = 379.2mi range in full tank. 410mi - 379mi = 31mi difference. If you can go 31 more mile with premium, that worth more than one tank of lower grade gas (since a gallon of lower grade gas give you 24 miles per GALLON), so it'll be +$4 saving there. But, savings from low grade gas can be calculated as follows: [(15.8 x $4)-(15.8 x $3.80)]=3.16 ---a saving of 3.16. There's roughly a dollar more saving for using premium gas.
This is purely from my experience with my e90. My e90, 2006 330i, has more than 2mpg diff when using low grade gas. Not apple to apple, but just wanted to share this.

[HighlandPete]

Originally Posted by tony20009

I have to admit, I don't care about what folks think are the differences you noted. I only care what they have actually done and observed, and even with that, I'm not asking for folks to draw a conclusion about causality for their observation.

We'll see if that actually happens. So far it hasn't.

My comment was light hearted banter, not an answer.

I'll be serious. This is BMW's statement for 328i & 335i in the UK data.

BMW Recommends the use of RON 95 super unleaded petrol. Unleaded RON 91 and higher with a maximum ethanol content of 10% may be used. Output and consumption figures apply to RON 98 fuel.

Translate that to US ratings and you pretty much have your answer on a technical level.

So we have a lot of scope within the engine working parameters (knock sensing, etc.).

Now what we don't see is the long term effects of any particular fuel. If long term is not the concern, then total freedom within fuel specification.

Personally I have a bias towards our premium fuels in the UK, simply to get best performance from RON 97/98, plus in the UK we have a better additive/cleaning package to our premium fuels. For me that is what I'm buying into. I use my car locally, so anything that helps longevity, keeping injectors at peak performance and optimizes mpg long term is worth a few bucks more.

We will not likely notice any change in average day to day driving, using different octane fuels. I can't tell the difference in performance in my 535i, whether running RON 95 or 97 in daily driving, as the engine is not really worked hard. Mpg favours the RON 97. This is different to my 540i (NA engine) which definitely was better for output and mpg on the higher octane fuels, noticed even in daily driving.

Was speaking with a BMW specialist a while back and he was definitely of the opinion fuel does have a long term affect on engine performance, poor injection, even piston issues and wear, due to heat levels if driven hard on the lower octane ratings. He did expand his reasons to include poor quality fuel and we are talking the additive package element to the fuel as well. But most of us never see that negative side of fuel use, particularly if we change cars regularly.

What I do question is the reason why we'd want to use the lowest fuel grade? If it is for immediate cost savings, perhaps we do need to do the math, as already posted in other replies, (may not be the cheapest fuelling per mile anyway) and think longevity, if we are keeping our car to high mileage.

HighlandPete

[Elk]

As a performance data point, there will be only a couple percent decrease in power with lower octane. For reference, the Hyundai Genesis engine (direct injection, turbo, 2.0) loses 3% when run on 87 AKI v. 91 AKI. (87 AKI is approved in this engine).

No one will notice the roughly five BHP decrease in peak horsepower running 89 AKI.

[pallymore]

I always use Shell V-Power. To be honest I can't really feel the power difference between v-power and other fuel. (The first 2 tanks were BP mid-grade and premium). But I can see that V-power seems to be much cleaner than BP mid-grade.

The exhaust pipes went almost all black inside during the first 2 weeks. I had a detailer cleaned them and filled a tank of BP premium gas(my 2nd tank). The pipes went black again.(I know, it's normal). So when the tank was almost empty, I wiped the pipes clean and filled the tank with V-Power...the pipes are much cleaner after 2 weeks use.

[Meeni]

It's going to be fine using 89. I'd stay with 91 for the summer at least, but it's not going to explode on you. You should be more worried about the location of the gas station he goes, and how much ethanol they put in the supposedely 10% mix and if the tank is clean at the facilities. Using dirty fuel is much worst than using 89 or 91.

It is not obvious -at all- that higher octane get better mpg. Higher octane is obtained by mixing more ethanol, which has less BTU per gallon, so it may actually well result in decreased mpg, even though the valve timing is better. This is actually more in line with my personnal observations since ethanol gas has been introduced, but I refuse to make a statistic out of my sample of 1

[dalrx]

If you can afford to give your kid a new f30 then just give him money for free gas and tell him to fill it with supreme all the time , problem solved.

[tony20009]

Originally Posted by dalrx

If you can afford to give your kid a new f30 then just give him money for free gas and tell him to fill it with supreme all the time , problem solved.

I do, he's just trying to be thrifty and save where he can. I'm not going to chide him for that or discourage it. It's a good habit for him to adopt now rather than later when I'm not going to pay his bills.

[JasonX4MComp]

Hes trying to be thrifty so he can save money for more beer!haha

[bananachipz]

Originally Posted by tony20009

I do, he's just trying to be thrifty and save where he can. I'm not going to chide him for that or discourage it. It's a good habit for him to adopt now rather than later when I'm not going to pay his bills.

Interesting.

You do have to admit, that buying a new BMW, then trying to be thrifty on gas seems odd. Not judging at all, just pointing out why others would be a little snarky in their responses.

Out of curiosity, why didn't you just buy him a Diesel Jetta if thriftiness is of concern?

[B///MWGuy]

Originally Posted by bananachipz

Interesting.

You do have to admit, that buying a new BMW, then trying to be thrifty on gas seems odd. Not judging at all, just pointing out why others would be a little snarky in their responses.

Out of curiosity, why didn't you just buy him a Diesel Jetta if thriftiness is of concern?

I don't think being thrifty on gas is wrong. OP's son is student, and I understand (as I was college student not long ago) why his son wants to save as much money as he can.
My father owns his own business and is quite very successful. However, he is being extremely thrifty and he used to only used 87 for his 2012 7 series and previous BMWs until I told him that 91 is more fuel efficient recently. He has ability to buy a Ferrari but he thinks that is pure waste.
Look at Bill Gates and Warren Buffet, whom they can purchase a plane only rides economic class for their air travel.. Being thrifty is way you become rich and stay rich. So I think its good habit.

[Elk]

Originally Posted by bananachipz

You do have to admit, that buying a new BMW, then trying to be thrifty on gas seems odd.

Not at all.

If one can obtain the same result for less money spent, most would embrace the less expensive option.

The OP's question directly addresses whether the result of using AKI 89 is the same and whether there is a hidden downside. Completely reasonable.

[tony20009]

Originally Posted by Jason335iMsport

Hes trying to be thrifty so he can save money for more beer!haha

That's probably correct. It's what I would do....

[tony20009]

Originally Posted by bananachipz

Interesting.

You do have to admit, that buying a new BMW, then trying to be thrifty on gas seems odd. Not judging at all, just pointing out why others would be a little snarky in their responses.

Out of curiosity, why didn't you just buy him a Diesel Jetta if thriftiness is of concern?

I don't have to admit that at all. What would make you think that buying a BMW and being thrifty about gas are incongruous?

I am the one who bought the car, my son is the one who received it. You might note that I'm not the one trying to be thrifty; my son is. I'm merely supporting his expressed interest.

I didn't buy him a diesel Jetta because I wanted to give my son a BMW, not a Jetta. In providing material things for my family, I give to them nothing less, and sometimes (but not often) more, than I would provide for myself. That's just "how I roll."

The boy has more than enough money in his spending account to afford premium gas, and beer and road trips and whatever else he wants -- within reason for I know I've not provided him with enough to jet over to Monaco every month. This is his inquiry, not mine, and it doesn't bother me in the least that he wants to save a dime here and there where he can.