# From Premium Gasoline (93 octane) to Silver (89) to Regular (87)



## shamilot (Apr 30, 2004)

I've been pouring premium gasoline into my car (brand new 325CIC) ever since I drove away from the dealership in June. The owner's manual reccomends premium gasoline 90+ octane. But, people have different opinions on whether or not higher octane makes a difference (except of course in $$). Like someone said about vitamins once that the only thing they do is give you expensive urine.
It's my only car so I drive it everywhere: work, school, shopping, dates, weekend excursions to the country, etc.. I'm not an aggressive driver by any means on the contrary I've been criticized by my friends for babying such a powerful sports car. 
My question is: will downgrading octane at the pump to at least Silver (89 octane) do any harm to the engine or other related parts? If not, can I go as low as regular (87 octane)?
Also, if I stop using premium will the manufacturer's warranty become null? (true, no one has to know... unless of course there's a way for them to find out). And finally, what if I alternate each time I fill up the tank between premium/silver, silver/regular, premium/regular?
Hey, with gas prices the way they are every penny counts. (this car is a gift so that's how I can afford it). :angel:


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## shizat63 (Feb 14, 2002)

The computer will change the VANOS timing to compensate for the lower octane, otherwise you would get detonation and eventually damage.

Dude, go back to 91 :tsk: This is precisely why I won't buy a pre-abused car


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## jgrgnt (Apr 27, 2002)

Figure $0.20 difference between regular and premium.

For a 15 gallon fillup, done four times a month:

$0.20 x 15 x 4 = $12.00

x 12 = $144 a year.


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## Lanc3r (Sep 5, 2004)

If you take into consideration that the fuel in Europe is rated higher octane( even though its rated with a different formula) I wouldnt go down to 87 octane unless I drove a Ford. The higher octane fuel burns easier, cleaner, and more efficient. If you truly Baby your bimmer, giver her the good stuff.


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## Desertnate (Mar 11, 2002)

Not only are the financial gains minimal, but you will see other problems as well. I had a tank of 89 "accidentally" put in the tank (it might have been 87...the wife doesn't remember) and this is what I noticed:
- rough idle
- poor throttle response and reduced hp
- lower mpg
- engine just seemed to run rough at all throttle positions

When I was able to find out what happened and put a good tanke of gas in the car it was a whole new machine.

Do a search here on "octane" and you should find a large number of threads that discuss this topic a length.


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## Stuka (Jul 17, 2002)

Sell the car and buy a Honda Civic.  

If you can't afford the few $.15 additional per gallon, you are driving the wrong car, period, end of story. :thumbdwn: 

Driving a nice car is great, but not great enough that you should sacrifice your financial well being for. :angel:


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## Nick325xiT 5spd (Dec 24, 2001)

The loss in fuel efficiency generally makes up for the cost savings. Since you also lose a lot of power, this seems hard to justify.


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## Miles_1 (Jul 26, 2004)

Use what the manual recommends. However, whatever you use the engine management computer will compensate. When I had my Porsche which required 93 octane because of a higher higher compression engine than my 330, I was reading an interview with a Porsche engineer in Christophorus (Porsche's official magazine). When asked about octane, because 93 octane isn't available in some places, he said that under normal driving conditions, a person likely couldn't tell any difference even if they were using 87 octane. The car would have a very slight degredation of performance and that would be all.


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## Staszek (Jan 28, 2004)

In an average car you are correct, if you are driving a basic Ford, Toyota etc, putting 87 or putting 93 in will not make a difference, but.........

in your car BMW has set the timing up for the higher octane, you will definetly see lower performance as the Vanos adjusts to the lower octane and eventually if you do this for to long it may cause some damage. For the amount of money you will save its absolutely not worth it.


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## palooka666 (Apr 23, 2002)

I also find that lack of a tiny bit of throttle response tends to make you use more fuel, so i actually think it works out the same since i find myself being a little more lead footed trying to get a little better performance out of a car.



Staszek said:


> In an average car you are correct, if you are driving a basic Ford, Toyota etc, putting 87 or putting 93 in will not make a difference, but.........
> 
> in your car BMW has set the timing up for the higher octane, you will definetly see lower performance as the Vanos adjusts to the lower octane and eventually if you do this for to long it may cause some damage. For the amount of money you will save its absolutely not worth it.


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## andy_thomas (Oct 7, 2002)

misterlance said:


> If you take into consideration that the fuel in Europe is rated higher octane( even though its rated with a different formula) I wouldnt go down to 87 octane unless I drove a Ford. The higher octane fuel burns easier, cleaner, and more efficient. If you truly Baby your bimmer, giver her the good stuff.


Actually fuel with a higher octane number is more difficult to burn, not easier. If it was, picking (pre-detonation) would be worse with a higher-octane fuel.

My car has double VANOS, and Valvetronic. It is designed to run on 95 RON, which is broadly comparable to about 90 AKI. Its power and economy figures are quoted assuming the fuel tank is full of 95 RON, and the manual recommends 95 RON for best performance, although right down to 91 RON (86 AKI?) is acceptable if that is all that's available. In my case, putting in 98 RON - one grade higher - makes absolutely no difference to power, economy or engine running characteristics.

BMW's six cylinder engines in the European market are designed to run on 98 RON. If you only put 95 RON in, performance and economy will suffer accordingly, and IIRC 91 RON is *not* recommended. At £0.88 a litre for 98 RON, I am glad not to have this burden!


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## Jim Seattle (Dec 20, 2001)

I'm not a machanic nor do I know as much as some of these guys do about this, but I use the cheap stuff and I get great gas mileage...and it keeps getting better. I've had no problems, doesn't idle rough, and the performance output suites my drive needs. I have a 323Ci with 35K on it. So it basically boils down to how much cash you want to pay the man. And like the guys said...it's not that much more to use the good stuff. But having said that...I still use the cheap stuff...


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## JRJOHNKC (Jun 6, 2004)

Dealer said 89 was good to go... Mine runs just fine on it. Runs great actually. I wouldn't go down to 87 though.


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## streetk14 (Oct 16, 2004)

Like some of you guys said, you aren't saving that much money by buying cheap gas. I put 91 (the best they offer here) in my cars, and I fill up at probably the most expensive station also (76). If you are driving a car that is designed for premium, run premium. Also, I don't think that the vanos adjusts the cam timing to compensate for octane. The DME uses knock sensors to sense detonation, and will pull out several degrees of timing until the knock disapears. Then it will gradually advance back to it's normal setting (assuming no detonation is noticed). This protects the motor, but you will notice a loss of power and throttle response. This was very noticeble on my girlfriends E36 325. switching from 89 to 91 has made the car more responsive, and we both have noticed this driving the car. Anyways, to each his own I guess.


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## marcelgood (Jan 24, 2003)

I believe the engines get tuned for each market to run best with the highest commonly available grade without knocking. So, if a car ships to a country where 89 is the highest available grade, the timing is already retarded from the factory, so that the engine doesn't knock and the hp rating will be adjusted accordingly. The problem with knock sensors is that the engine has to knock first before the they detect the knock. This is good for the occasional low grade or bad fuel, but why somebody would deliberately cause the engine to knock with lower grade if the higher grade is available is beyond me. I don't know if the DME keeps the retarted timing when you turn off the engine, but if not, your engine knocks everytime you turn it on for the split second it takes the DME to retard the timing. I might be wrong, but this is my educated guessing.


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## Gabe (Sep 20, 2004)

There are some misconceptions floating around this thread. Check out: http://www.howstuffworks.com/question90.htm



How Stuff Works said:


> The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.


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## LeucX3 (Dec 26, 2001)

JRJOHNKC said:


> Dealer said 89 was good to go... Mine runs just fine on it. Runs great actually. I wouldn't go down to 87 though.


Runs fine, yes, but probably not optimal.


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## shamilot (Apr 30, 2004)

*interesting responses and link 10% Ethanol in gas?*



Gabe said:


> There are some misconceptions floating around this thread. Check out: http://www.howstuffworks.com/question90.htm


Great link, thanks! 
The station where I usually fill up near my house has stickers on their pumps that read "Contains 10% Ethanol" what does this mean?


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## Gabe (Sep 20, 2004)

shamilot said:


> Great link, thanks!
> The station where I usually fill up near my house has stickers on their pumps that read "Contains 10% Ethanol" what does this mean?


To answer this question, check out "How Gasoline Works"

http://www.howstuffworks.com/gasoline4.htm


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## Crawlings (Sep 27, 2004)

So, will it hurt your BMW to put higher octane gas in it than is recommended? For instance, if I do the European Delivery on one which gas should I use? They tend to have higher rated octane, or a different rating all together, correct?


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