Hello,
I have read many times in Consumer Reports (and similar) that paying extra for premium gas is a waste of money. Is it really necessary for me to run premium in a 2006 BMW 325 wagon with 100k miles on it? Thanks in advance.
It’s a waste of money if the car doesn’t need premium, that’s what all those articles say. Some cars need it because of their engine design. What, exactly, does your owners manual say?
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CR says it’s a waste of money if your car is designed to run on regular. See what your owners manual specifies/demands/suggests/recommends.
If premium, then use premium unless you are willing to experiment with regular. Your car will probably be just fine on regular, with a slight reduction in power and smoothness under heavy acceleration or engine lugging. That’s because the engine control system will compensate for any preignition by retarding the spark timing a little bit, That results in a temporary reduction in power, compatred to what the engine can produce with premium.
In sum: premium won’t make a car designed for regular run better. It will enable a car desuged for premium to achieve its maximum power.
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But, additionally, that slight retarding of the spark timing will also reduce the gas mileage, so instead of saving money it is possible that there will be little or no cost saving on gasoline in the long run.
That reality, coupled with the reduction in power makes this a questionable decision, IF the car’s manufacturer states that premium gas is required.
So, just to reiterate what has already been stated, the answer to the OP’s question lies in the Owner’s Manual.
The correct answer is as close as the car’s glove compartment.
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They don’t know where the glove compartment is as it’s location is identified in the owner’s manual.
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Yup, you need premium, check your owners manual. As others have said if your car requires it, like yours you need to buy premium. If premium is recommended you may gain a bit, if regular is recommended you gain nothing
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I don’t think the OP would have posted here if he didn’t read somewhere that his car needed premium.
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Is premium recommended or is premium required there’s a difference there. Per the owner’s manual ;
Required fuel
Premium Unleaded Gasoline
The minimum octane rating is 91.
If you use gasoline with this minimum octane
rating, the engine may produce knocking
sounds when starting at high outside temperatures.
This has no affect on the engine life.
It would appear that your car requires premium fuel. What CR suggests is that some manufacterers recommend premium fuel, but the car will function on regular without risk of damage or anything. My car will run on 87 octane fine, but in order to get the advertised horsepower and fuel economy, premium needs to be used. In your case premium is required, not suggested.
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FoDaddy nailed it./ Page 25 of the owner’s manual plainly states REQUIRED FUEL Premium Unleaded Gasoline.
Look at it this way. You’ll probably spend $20 to $30 extra every month having to use premium gas. If you can’t afford $20 to $30 a month, then you shouldn’t have bought a BMW.
Buy premium, mash the gas pedal and enjoy.
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Check whether your car enriches the fuel mixture to avoid knocking. If so, running lower than require/recommended octane could reduce the life of the catalytic converter cutting into the savings from using lower octane fuel.
The fuel door has a sticker of fuel octane or type recommended or required.
Check you mpg if downgrade. On my vehicle a 2007 Acura MDX there is a noticeable drop in power AND a mpg loss using regular that if you normalize the cost it’s turns into a wash.
With regular if loaded it tends to shift considerably more to keep speed on grades.
The perception is that if the car is capable of compensating for the use of other than premium fuel than buying premium fuel will be a waste of money. It’s false reasoning.
The engine compensates by sensing engine activity (pinging, via its knock sensor) that is a side effect of too low an octane. It does so by retarding ignition timing, and in some engines perhaps adjusting the pulsewidth of the injectors. These reactions to the sensing of the engine doing something it shouldn’t compromises performance and may not save any gas at all. What it does do is compromise engine efficiency. And if your owner’s manual says it’s REQUIRED, than using regular may even cause engine damage. Engine damage from pinging can result in a hole in a piston… or two. That’s your risk. The choice is yours. Hundreds of thousands of miles of fun driving in the car that you paid so much to get premium performance in, or compromised performance possibly resulting in blown pistons. The choice is yours. 
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Even if premium is recommended not required I would use premium. That is what the car is designed/tuned to use. Your car will thank you with proper performance and engine longevity. In your case with premium required you would be a total fool to use regular.
The fear mongering of holes in the pistons is too much. Do you guys really believe a BMW can’t adapt to lower grade fuels?
I’ve actually seen it happen with my own eyes. Back when I was working for Ford. There was a guy who threw a hissy fit when his warranty claim was denied on a Lightning pickup. It wasn’t running well at all, he brought it in, and it turned out there was a hole in one of the pistons. The owner had been using 87 octane on a vehicle that required premium (supercharged V8) he didn’t think it would make a difference. Turns out it does, and he had to foot the bill for the repair.
It was a sight to behold, the guy was making a scene, the only reason I happened to see it was because I heard the guy yelling at the service advisory, the manager, and the mechanic. Apparently he wouldn’t take “no” for an answer and was in the midst of working is way up the chain of command. They guy was pretty livid, and wasn’t having it, even though the service manger got out the owner’s manual and pointed out where it said that the truck required 91 octane or better. I’m not sure what the outcome of that episode was, but it went on for a while, I watched for about 20 minutes and nothing seemed to be resolved.
On my mother’s Benz, the manual actually goes into detail on what you’re supposed to should you for some reason need to put 87 octane in it. You’re not allowed to give it more than half throttle, the engine speed should not go over 3000 RPM, you’re only supposed to put 1/4 tank of 87 octane at most and then fill up with premium as soon as possible. It’s hilariously specific.
Nevada, are you suggesting that the owner ignore the manufacturer’s requirement and drive happily into the future using regular? That there’s no risk?
FWIW, the reason why premium is suggested or required by the manufacturer is b/c of the compression ratio of the engine design. It’s probably higher than most cars. My truck for example has an 8.2 compression ratio. Your BMW is probably more than 10. The advantage of a high compression ratio is a more powerful engine for the size and weight. Faster 0-60 times in other words. The disadvantage is it requires a higher octane gasoline to work correctly. If it were my car I’d use what the manufacturer recommends.
That is how it was 40 years ago. The Prius engine is capable of 13.5 to 1 compression via the Atkinson cycle engine but uses regular fuel. Regular fuel is generally chosen by manufactures for economy cars, a Corolla might get 1-2 MPG more if it was designed to take advantage of premium fuel but customers would shy away because of the premium fuel requirement.
Upscale cars are designed to take advantage of premium fuel for competitive reasons, horsepower and fuel economy. If the vehicle used premium fuel during EPA certification testing the owners manual must state “Premium Required”.
People don’t always use the correct fuel. I have drained diesel fuel and E85 from many tanks, I suspect there may be 20% of vehicle owners that pay no attention to whether they are pumping regular or premium.
FWIW we have a toyota sienna with the 3.3l engine, it only requires 87 octane but specifies that the engine is designed to take advantage of higher octane fuel.
I have tried running 93 octane in it for several tankfuls and noticed little power or mileage difference, but I usually drive it pretty easy anyway.