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Time to dust off my old car mechanic hat from 25 years ago. I am no chemical engineer, but it is my understanding that the higher the octane the more stable the fuel is when heated and under pressure and the cooler the burn. Hence, engines with higher compression ratios (hotter air/fuel mixture pre-spark, more efficient combustion post-spark) actually get more power from premium fuel. The general rule of thumb (my thumb has been getting quite a workout these last couple of days) is to use the lowest grade of fuel that your engine was designed for.
With modern ignition systems, that rule has gotten a little fuzzy, but it is still a good idea to follow it for several reasons:
The earlier your engine can fire the spark plugs relative to the position of the piston the more heat you generate, the better the thermal efficiency. The better the thermal efficiency, the more power you get from a given amount of fuel, that yields either better power or better economy (or a combination of both).
Ignition systems can only retard so far, if you have a very high compression engine (10.5:1 or better) you may actually damage the engine by using a lower grade of fuel in anything but "Limp Home Mode". That means that if you have no other option, use the low octane fuel and then yield to the Little Old Lady in the 1975 Granada.
Higher-grade fuels usually have extra detergents and other additives that help your engine stay clean and produce full power for a long period of time.
A few years ago, it seemed that the reverse situation was happening, people would buy a fairly pedestrian automobile that was designed for low-grade fuel and then put Premium in it. The thinking was that Premium would give them better power; this cannot be farther from the truth. In reality, the low compression (8.0:1) will not generate enough heat to assure complete combustion of the stable high octane fuel, this results in deposits made up of combustion by products being left all over the inside of the combustion chamber and the valves. If the driver persists in using Premium on such a car, it would become a self-fulfilling situation. With enough deposits, one will eventually form as a small narrow spike, it will get hot and start glowing, then, the only way to keep from blowing a hole in a piston or blowing a valve up into the head is to continue using Premium. Eventually, even that will not be enough. I seem to remember a guy over at the local airport filling up his Yugo with 100LL aviation gasoline. ;-)
Brave1heart,
;-)
Best Regards,
Shipo
This was an interesting tech sessions on fuels though. Glad we have such a wealth of knowledge here.
Filling up a Yugo with 100LL aviation gasoline - LOL. That's classic of the same caliber as that guy who called technical support to complain that the cup-holder that his PC came with just broke. Yep, it was the CD ROM he was talking about and it was a true story, just like the Yugo.
deepdarkblu,
I don't know how much of a difference it's going to make if I'm awaiting a 325i, but I know that my dealer had the purchase request in on 5/17, a Thursday. By 5/22, my car was already in 151 status. It is now in the paint shop and due to be completed by 6/8, if not earlier. It's 2 weeks ahead of the proposed schedule.
I know there was a discussion on 325s produced at the South Africa factory, right, and I didn't mark anything, unfortuantely. I'm even unsure where my car is being produced...still. I think I will give BMWNA a call again. BUT, if it is being produced in SA, is there anything I should be aware of. Has anyone here had one produced from it and were even the slightest concerned. I don't think I should be.
good luck on the sound system. Let us know you like it.
Dinan's chips ( as well as conforti and others ) work partially because they advance the spark, which requieres premium.
If i were driving like a nut on a very hot day, i might fill it up with premium.
Write a book? Thanks. I think fiction and computers are my game.
dave
in this part of th country are lower than what's
found in Houston for example.
On my first test drive of 3-Series here in
Albuquerque, the salesman specificly stated that
all their vehicle used and were filled with
regular 85 octane. When I pressed him about what
the factory recommended he still insisted that
regular was adequate and the dealer stood by that.
Which is why we should all use the minimum octane that the engine is designed for (91 for 3ers, I believe)...
http://www.bimmer.org/3series/messages/archive/msgsy2001w22/34968.html
So, have we figured out the optimal octane rating for our 3ers? If it's 91, then I'm pumping in a couple octane ratings too high and wasting a couple dollars/month in the process. I don't care about the extra $5/month, but I DO care about engine longevity and performance optimization! Is it 91 or 93??? Shipo -- you seem to be the most knowledgeable about this topic -- any further insights?
I love the car and I don't think I have any problems with it, but the more I think about it, I think I could.
Anyway, I've driven standards for 10 years; honda, nissan, mazda, ford... All of them have been easier and much smoother than the BMW. I am not sure if it is because it is rear wheel drive or what, but when I shift, the noise is loud, like a clunk and it is rarely smooth; at least from 1st to 3rd gear.
So, this gets me thinking... is this normal? I don't remember the car I test drove to be that "rough", but it has been 9 months or so.
I have read comments where people have said the car needs to be broken in, etc... and things only get better. Well, 15k miles later and mine doesn't appear to be getting better.
Not only that, but does anyone have a hesitation when pressing the accelerator? Sometimes, the car just doesn't want to move. Where is all the power?
Okay guys (and ladies) help me out here. Am I paranoid? I'd like any suggestions so that when I take the car in on Saturday I can speak to the service advisor with some knowledge of what I am talking about.
Suggestions are welcome... appreciate it.
Thanks,
Stacy
Thanks.
That said, however, I do remember reading a post a while back stating that use of 93 octane does increase fuel economy, so it might just be worth spending the few extra cents per gallong after all.
As far acceleration, there isn't a whole lot of it under 1,800 RPMs - you should specify what RPM level you feel that at.
BTW, I love your 'Mods and Music' motto. It's almost like the Romans' 'Bread and Circus'!!
When I drop my car off for service, I was going to see if I could drive another 330 to see if there is a difference or if I am paranoid.
In all seriousness though, it just doesn't seem "normal". (Then again, what is normal?)
Stacy
Given the current auto market conditions and the fact that MY 2002 cars are soon to come, I would anticipate dealers to loosen up a bit over the next few months.