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I have 1999 323i and the manual says that premium unleaded should always be used, especially for 6 cylinder engines, and that regular unleaded should only be used in "exceptional circumstances".

I know in most cases it's best to do what the owner's manual says however I have read numerous articles and studies that state the only difference between regular and premium unleaded fuel is an additive in the premium fuel that stops pre-ignition (also known as engine knocking or pinging).

The articles all seem to conclude that unless your car really needs premium fuel (eg. if it's turbo or supercharged), it is just a waste of money because there are zero performance or mileage gains to be had by using fuels with higher octane ratings. Conversely, I heard a performance tuner say one of the general rules of performance tuning is that you should always use the fuel with the Lowest octane rating which the vehicle can handle without knocking.

To add to all this confusion, I have heard countless conflicting testimonials from people who swear by premium whilst others who say regular unleaded actually gives their vehicles (not just BMW's) better performance.

What do you guys think? Do you notice any difference between regular and premium unleaded? What should I use in my 323i?
 

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Keeping it surreal
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Use the best fuel available....there`s a ton of documentation which proves that the benefits outweigh the extra cost. If you can`t afford the proper fuel, sell that BMW and buy a Corolla....
 

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Discussion Starter #3
I can afford it. that doesn't mean I want to pay for it if there's no benefit in doing so.

Also, the corolla costs more

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I can afford it. that doesn't mean I want to pay for it if there's no benefit in doing so.

Also, the corolla costs more

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Unfortunately, that is the cost of owning a BMW. You MUST use premium fuel, as lower end gas can and WILL cause issues to your engine down the line. Loss in performance in addition to lower MPG if you use regular gas. Stick in some fuel additives and your MPG will improve. Never and I repeat NEVER under any circumstances put regular gas in your BMW. In addition, in some places the regular gas will only save you a few bucks, no more than $4. Yes, great to save, but when it comes to your car you must think about the long term of engine.
 

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I have 1999 323i and the manual says that premium unleaded should always be used, especially for 6 cylinder engines, and that regular unleaded should only be used in "exceptional circumstances".

I know in most cases it's best to do what the owner's manual says however I have read numerous articles and studies that state the only difference between regular and premium unleaded fuel is an additive in the premium fuel that stops pre-ignition (also known as engine knocking or pinging).

The articles all seem to conclude that unless your car really needs premium fuel (eg. if it's turbo or supercharged), it is just a waste of money because there are zero performance or mileage gains to be had by using fuels with higher octane ratings. Conversely, I heard a performance tuner say one of the general rules of performance tuning is that you should always use the fuel with the Lowest octane rating which the vehicle can handle without knocking.

...
BMWs are tuned, and run on the EPA mileage and emissions tests on premium fuel. You get benefits of better mileage and more power by running premium.

(Not sure about the 323i, but) all BMWs since at least the M54 have knock sensors that allow you to run regular, but mileage and power go down.
 

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I can understand managing running costs. That being said you are coming to a community where the regulars are borderline fanatics who care for their cars greatly and provide them with whatever is needed, almost to the cost no object point. Asking about regular vs. premium gas is borderline heresy; the cars get the good stuff - period.
 

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Discussion Starter #8 (Edited)
Olga: firstly, the e46 is a used car. If you're reading this section you ain't no baller so don't kid yourself. Secondly, fuel prices vary across the world. If you have nothing of value to add, why say anything at all?

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Discussion Starter #9
Fredoin: Exactly. I want verifiable facts not hearsay.

A while ago Toyota said something to the effect that all Toyotas must use Toyota branded coolant which is bollocks.

I want to know whether my 323i knows the difference between premium and regular or whether its more of a placebo effect on the drivers. If I didn't care about my car I wouldn't bother asking the question would I?

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Olga: firstly, the e46 is a used car. If you're reading this section you ain't no baller so don't kid yourself. Secondly, fuel prices vary across the world. If you have nothing of value to add, why say anything at all?

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baller?? What strange talk is that. Anyway if people can't afford decent fuel get a Honda...
 

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Discussion Starter #11
I've owned 3 Hondas actually. Probably had more vehicles than you have underwear

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There are a number of issues after prolonged driving on regular vs premium fuel. One is the emission control system. While the ECM will compensate for the lower octane and prevent engine killing detonation (knock), it does so by introducing more exhaust gas into the system. The first casualty is the EGR valve. Issues begin to develop after just a couple of tanks and progress to the point where the car will not pass emissions tests. Just replacing the EGR valve usually doen't fix it. It takes a complete cleaning of the exhaust gas routing system. (expensive). Sometimes this happens very quickly. Our daughter put a tank of regular in my wife's car (supercharged) and the check engine light came on within a week. (code p0406). You can get away with using the mid-grade, but if you care about your car and plan on keeping it. Use the good stuff.
 

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Discussion Starter #13
Well forced induction engines such as your wife's supercharged one needs higher octane fuel ("the good stuff") but my 323i is naturally aspirated and I believe the knock sensor compensates for the lower octane by advancing the ignition timing. Not trying to argue, just looking for an answer as justified as those fuel articles I read.

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Ok this is my understanding as someone who googled my way through the topic before I bought my BMW. The octane rating is basically the engine knock resistance rating, the higher the rating the more compression that the fuel can withstand. The piston goes up and compresses the air fuel mixture and when it is the right position the spark is introduced. When a car has higher compression ratio it is possible to for the fuel to combust on it's own if it has a lower octane, because the temp can get too high under the higher compression (kinda how a diesel works). Compression combustion works in a diesel, but for our cars that use a spark it can create issues in the engine cycle. When the air fuel mixture combusts it pushes the piston back down, so you can see why early combustion could create a problem. Typically speaking with a ratio of 10:1 or higher you want to run premium, our cars meet that. There also have been probably countless number of studies that show in cars like ours the premium fuel leads to lower exhaust temps and better performance. There was one study in particular conducted by shell (take it as you will) where they took a Euro, American, and a couple Asian cars and in the Euro acceleration turned out to be about 4% faster, as well as exhaust temp was about 16 degrees cooler. I definitely recommend checking out some studies for yourself.

Now I am sure that there are plenty of people on the forum who regularly use regular fuel and have never had a problem. I am also confident that if you were to use regular there is a good chance that you might not ever have a problem either. That being said even if you don't ever have any catastrophic engine cycle timing issues you will at the very least be sacrificing performance. That is just my understanding of everything I read from probably a couple dozen sources back when I first bought the car though. I recommend doing some research though because all of us will mostly just be reciting the things we have read anyway, although there are some here who really have an understanding for this stuff.
 

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Modern engines de-tune themselves when they start pinging. So, even if you don't hear pinging, performance and fuel economy is decreased. Performance European cars tend to require better gas and oil. Designing their cars around better gas and oil are two ways they get the better performance. Even my cousin's Smart requires premium and synthetic oil.

Economy brands (Honda, Toyota, etc.) design their engines to tolerate 87 AKI. Requiring premium gas would annoy their customers. My cousin complains about her Smart needing premium gas.

I could tell the difference between 87 AKI and 91 AKI in my Chevy pick-up truck, especially going up a hill.

My 2014 BMW says it needs 91 AKI. They don't sell that here, so I make my own: 1/3 87 AKI and 2/3 93 AKI, saving about $0.20 gallon. I have a series of 1000 mile road trips coming up soon. I might do some 93 AKI vs 91 AKI field testing. If the MPG goes up with 93 AKI, I'd pro'lly go with that in the future instead of "Autoputzer's blend."
 

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i have a 98 lincoln continental and on the gas cap it says "premium recommended", I usually put regular on it and notices that it lacks power and gas mileage goes down compared to using premium. I also have a 02 lincoln ls that says "premium required" and although I haven't used regular on this one, the warning label clearly indicates it.

"recommended" and "required" are 2 different things.

also note that most premium fuel don't have ethanol mixed in compared to regular and although the car runs fine (underpowered) you won't know the long term effects on picky engines. even if you save on a tank of regular the drop in gas mileage will probably break even when using premium.

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My cap (not sure on yours) says unleaded fuel only. Now I have never tried any lower fuel (not even 89). However if your car takes 89 then (duh) you can put in 91. It'll get better mpg smoother acceleration etc. my Nissan that had before this, I'd put 91 and notice a pretty decent change.
 

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It's not just about octane ratings to prevent detonation:
"Six automakers, BMW, General Motors, Honda, Toyota, Volkswagen and Audi, believe using Top Tier Gasoline that contains a higher-percentage of detergent additive from that required by the EPA standard, provides optimal engine performance. They claim that lower concentrations of detergent additive lowers the quality of gasoline and can leave deposits on engine parts, such as fuel injectors and intake valves, which can lower engine performance, vehicle responsiveness and increase emissions." TrueCar 2011 Even the top tier gas companies only put the best additive package in the premium gas. That's reason enough for me to use it.
 
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