[tony20009]

I bought my kid a 328 F30. He called me this a.m. asking if he really had to put premium gas in it. I told him if he wanted to save some money, he could fill up with premium one time and then going forward, upon the needle showing half full, top it off again with mid-grade octane fuel. I said further that that so long as he keep refueling at the half full point, he could alternate back and forth and be okay, but that if he falls below half, he should only refill with premium.

He doesn't want to do that. (This shouldn't surprise you or me; kids always just want to do it their way, even when they ask and you tell them something other than what they had in mind.) He just wants to use mid-grade all the time.

So, if anyone here has tried using mid-grade all the time, have you observed any ill affects from having done so?

I've read a variety of stuff on the Internet about this matter, (http://usatoday30.usatoday.com/money...emiumgas_x.htm among others), but I'm interested in what real owners here are experiencing (not what they think, surmise or believe) from having done so.

[34.50]

I wouldn't recommend it - it may be cheaper in the short term, but can cost you a lot more in the long run. Using lower grade gasoline can cause engine knocking and your mileage will probably degrade.

[Tsuyoi]

Ultimately using the high grade fuel will be cheaper, since you'll both get a) more mileage from it and b)save undue wear and tear on your engine. If your kid wants to save some money, tell him to try running it on eco-pro in the city/burbs, and only shifting to sport when he has some open road. I used to average 23 mpg on comfort/sport when I first got my 328, but once I got the "new car rush" out of my system and started driving eco-pro more in heavy traffic/stoplight areas, i've bumped it up to close to 30 mpg.

[drob23]

I don't agree with the above, the engine knock sensors will inform the ECU to adjust timing accordingly, you won't do damage to a modern engine like the N20 with regular octane gas. You will sacrifice some performance in the high RPM band, and the engine will run slightly more inefficiently. I was told this a while back by some researchers working on HCCI stuff at a University.

The only caution I'd add is to run the same type of gas. The ECU will adjust these parameters over a windowed period (maybe a tank or two), so changing the octane level up and down with an eyeball cocktail is not the way to go. Just tell him to stick with 89.

You ask for solid advice, but I think unless you speak to an engineer who works on combustion systems or maybe a mechanic who's active these days, everyone is just going to give you whatever black magic theories they have. How can one reasonably discern whether the octane level is truly affecting anything? Only thing I can think of is people drag racing their cars or mayyybe claiming fuel economy differences.

[Bimmerfestool]

If I was your kid I would be happy enough to get a free BMW that I would probably pony up the cash for the gas that it requires.

[Cyberdemon]

Your first problem was not letting him drive a 92 Civic until he gets a job. LOL.

Realistically he isn't going to damage anything by running cheap gas, the car is designed to adapt to it.

With that said, he'll likely get worse fuel economy and certainly lower performance, especially when pushing the engine. If he's just lugging around town there won't be a significant difference.

Simple answer: Tell him if he wants cheaper gas you'll trade his car in for a Hyundai that takes 87....that should straighten him out right quick.

[HighlandPete]

Originally Posted by Cyberdemon

Simple answer: Tell him if he wants cheaper gas you'll trade his car in for a Hyundai that takes 87....that should straighten him out right quick.

Best answer.... and saves debating the differences (in use) of different fuels.

HighlandPete

[OC40]

We are talking about a difference of $1.60-$2.00 per fill up. He can save that by cutting out one coffee at his local coffee shop!

[samej]

Manual says 89 AKI - that's mid-grade so your car will be fine.

Here in Canada most mid-grades include ethanol, up to 10% - which can result in a 3-5% decrease in mileage. So filling up with premium (no ethanol) for 3-5% more is a wash.

[RoundelM3]

Again...saving $2 per tank just isn't worth the grief it might cause you if your engine develops problems and BMW finds out you've not been using the recommended fuel as it CLEARLY states on the gas filler.

[Elk]

Mid-grade 89 AKI is perfectly fine, as indicated in the manual.

Perhaps this is a good compromise

[Steve33]

Just run 89. No use for 91/93 if it runs fine on the recommended 89.

[BmwF30alpine]

Originally Posted by Steve33

Just run 89. No use for 91/93 if it runs fine on the recommended 89.

yup, unless your taking it to the track and have done mod's, just use what they recommend.

[IM2C]

Originally Posted by HighlandPete

Best answer.... and saves debating the differences (in use) of different fuels.

HighlandPete

[tony20009]

Originally Posted by Elk

Mid-grade 89 AKI is perfectly fine, as indicated in the manual.

Perhaps this is a good compromise

TY. Have you done it for any extended period of time?

Originally Posted by OC40

We are talking about a difference of $1.60-$2.00 per fill up. He can save that by cutting out one coffee at his local coffee shop!

I think both my kid and I can figure out how to make up 40¢, but thanks for your thought all the same.

My boy asked me a question for which I don't have much personal experience upon which I can rely to give him a very good answer, and I'm looking to collect some data and give him a better answer than I already did about what other folks have actually experienced by having done what it is he asked about.

Originally Posted by Bimmerfestool

If I was your kid I would be happy enough to get a free BMW that I would probably pony up the cash for the gas that it requires.

He is happy and, at the moment, to the best of my knowledge, he is just ponying up the extra cash. And since all the cash he spends is money I've given him, I know it's not really a financial burden for him, and he knows that too. I think he's just trying to be thrifty or he just wants to know in case it matters later when he's out of school and living on his own source(s) of income. And you know how college kids are, I presume. They are always looking for a short cut, convinced as they are that they know something the rest of us -- parents, car makers, politicians, Nobel Laureates, etc. -- don't. (Though admittedly, sometimes they do. Bill Gates did at that point in his life, but even for him what he knew still was rather narrowly focused, however profitable it turned out to be.)

Originally Posted by drob23

...

You ask for solid advice,..but I think unless you speak to an engineer who works on combustion systems or maybe a mechanic who's active these days, everyone is just going to give you whatever black magic theories they have.

I get what you mean, but actually, I asked for folks to share their experience, not their their opinions or advice. Yet opinions and advice are exactly what's being posted, as you anticipated.

Originally Posted by drob23

How can one reasonably discern whether the octane level is truly affecting anything? Only thing I can think of is people drag racing their cars or mayyybe claiming fuel economy differences.

I don't think one can, or at least I don't think a Johnny Regular Person lacking specialized equipment and whatnot can. But, at least for what I asked, one needn't draw any conclusions. One need only indicate (1) yes, they tried this or that non-premium octane gas for some period of time and (2) during that time or after, but never before, they observed this or that behavior.

But overall, you are right. It's very hard to get facts, even when that's all that's requested. Opinions are easy to come by, but as I have plenty of my own, I don't generally seek other folks' opinions. It's nice that folks share their opinions, and I appreciate the sentiment that accompanies their having done so, but that's not really helping me draw a conclusion for myself.

I can say that I one time filled my my E92's fuel tank with regular (87 octane) and drove it with no ill affects observed. I was in a small town -- more a village than a town, really -- that had one gas station and the other octanes were sold out. I wasn't going to drive over 120 miles to fill up on high test when I needed to be in that town for the whole week; it was just the decision I made. But that was one time. I was hoping to collect some additional data points.

[tony20009]

Originally Posted by HighlandPete

Best answer.... and saves debating the differences (in use) of different fuels.

HighlandPete

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.

[34.50]

Originally Posted by Steve33

Just run 89. No use for 91/93 if it runs fine on the recommended 89.

The US BMW site says Unleaded Premium for the 328i...

http://www.bmwusa.com/Standard/Conte...fications.aspx

Premium gas means 91/93 octane.

[tony20009]

Originally Posted by 34.50

The US BMW site says Unleaded Premium for the 328i...

http://www.bmwusa.com/Standard/Conte...fications.aspx

Premium gas means 91/93 octane.

TY. I too have read the manual, as has my child. That is why I asked if anyone had actually violated the instruction, and if so what they observed.

[34.50]

Originally Posted by tony20009

TY. I too have read the manual, as has my child. That is why I asked if anyone had actually violated the instruction, and if so what they observed.

Well, let us know how it goes.

[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.)

[Agamemnon]

I don't think you are going to get that answer from anyone on this forum. People on the forum are enthusiasts and are not about to take a chance on running low grade fuel in automobiles that they paid a lot of money for and appreciate. The car is turbocharged, has direct injection, runs a high compression ratio, etc - therefore high grade fuel is a must - thats why it is recommended.

Tell your son to run premium as stated by the manufacturer who made the car in the first place. You got many replies that are sensible - now give it up and run the right stuff or go buy a car that runs 87!

[tony20009]

Originally Posted by 34.50

Well, let us know how it goes.

Well, my cousin finally returned my call. She regularly puts 89 and 87 in her car, regularly as in from the day she got it back in 2010. Admittedly it's an E90 with a I6, and not a turbo 4, which is what my kid has, and I know there has to be some difference between the two engine's tolerance for differing octanes. However, I don't care to read -- here or anywhere else -- about what those differences could be. I just want to know if anyone's actually used 89 or 87 in their car.

She said she can't recall the last time she floored the gas. (I can vouch for this being true; she's drives so much like an old woman that it pains me to ride in the car when she's driving.) She said she hasn't noticed a single thing being wrong with the car and that the car's performance hasn't changed as far as she can tell. Odds are she could burn moonshine in the car and not notice a performance difference.

That's about what I expected her to say, and why I posted something here. I know my son drives a bit more assertively than she does and he has a different motor than she does, so I don't want to just assume that her experience will mirror his.

I also know my daughter is doing the 93, 89, 93, 89, 93 back and forth thing I suggested to my boy. She's detail oriented enough to keep up with it; he's not, and he and I both know it, which is part of why he asked in the first place. My daughter, however, also has an I6 (2010 E91 328).