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I have a 98 BMW 528 that I have always run with Texaco unleaded regular octane gas. I am intereted in purchasing a 2006 325 or 330 and was wondering if anyone is running anything less than the recommended fuel. I have a friend that has had several 740's and has always run them with regular gas.
 

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:wave:

Hi, and welcome to the fest.

The answers you get will likely fall into two camps, with (based on my subjective analysis;) ) about 3/4 of the posters using the manufacturer's recommendation, and about 1/4 using regular gas, because the engine "will adjust".

Personally I am ok to follow the manufacturer of the engine's advice. I use super unleaded.

rj
 

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Hey there... :thumbup: welcome... there are a bunch of threads on this topic... this would be a great time to practice the handy dandy "Search" feature. ;)
I recommend Premium.
 

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87 Octance or 91? - An explanation

From a purely technical viewpoint, if the manufacturer says that higher octane fuel is recommended, then go with their recommendation. The reason is as follows:
Many high-performance engines use higher compression ratios, in their cylinders. Combustible fuel (gasoline or diesel) spontaneously combusts (i.e. explodes in the combustion chamber or cylinder) if the temp and pressure are high enough. In the case of diesel engines, this is not a problem ..in fact that's the way diesels are supposed to run. But in petrol based IC engines, the spark plug provides the ignition of the fuel-gas mixture. so, if the cylinder temp and pressure are very high, and if you use low octane fuel, then there are two explosions in each cycle, instead of just one ...one explosion when the cylinder compression gets high enough, and another just a fraction of a second later, when the spark plug fires. This can damage the valves, since they are out of position, when the first explosion occurs. Btw, this is also know as 'knocking.'
You can prevent knocking, if you use higher octane fuel. In higher octane fuel, the explosion point occurs at a higher temp-pressure combination.
Most cars that use lower cylinder compression such as your GM/Honda, etc, can therefore use lower octane gasoline (petrol). In those cars, using a higher octane fuel gives you NO extra benefit.

Another phenomenon that can occur when using a low octane fuel in a high compression engine (in BMWs and Mercedes) is 'pinging'. Knocking and 'pinging' are basically the same thing; knocking is louder and represents a more serious condition. When they occur, it is during acceleration, though higher engine speeds tend to drown them out. Knocking sounds like someone repeatedly rapping the engine with a hammer, and the quieter pinging resembles marbles being shaken inside a tin can.
Having said that, in respose to earlier suggestions that you can run your BMW on regular octane petrol, I now direct your attention to the following important information ..
I quote the following from a tech source
"Most modern, computer-controlled engines include a knock sensor that detects knock and retards the ignition timing, causing the spark plugs to fire slightly later in the cycle. This typically prevents abnormal combustion and knock, which allows vehicles specified for premium fuel to run on lower-grade gasoline if it is all that's available. While this removes the immediate hazard, it's a bad idea to make a habit of running a vehicle on gasoline of lower-than-recommended octane. Retarding the spark causes a richer fuel/air mixture, which decreases fuel economy, increases emissions, causes the engine to run hotter, and reduces the longevity of both the engine itself and the catalytic converter. The money you save by pumping low-grade fuel into a car that demands higher octane is lost anyway, in decreased fuel economy and possibly gradual damage."

And finally,
"Your vehicle's owner's manual usually recommends an octane rating in terms of an Antiknock Index (AKI), which also is posted on gasoline pumps. The AKI is the average of two ratings determined in a laboratory: the Research Octane Number (RON), which corresponds with low-speed, mild-knocking conditions, and the Motor Octane Number (MON), which covers high-speed, high-temperature knocking conditions and part-throttle operation"

Hope that answers your question!
If you own a BMW/Merc, don't listen to the morons who want to try to save you money by suggesting that you use a lower octane fuel. Just as important, if you own a standard issue GM/Honda/Toyota, ignore the morons that say that you can get better performance by loading it up with premium gas. That simply isn't true.

Cheers.
 

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SammyK....excellent explanation !!

Additionally, it's interesting to look at the "savings". Let's say you drive 15000 miles per year and average 20 mpg. That means you purchase 750 gallons of gas per year. The difference between premium and regular is usually around 20 cents per gallon, so that means the "savings" is $150 per year. Is it really worth it, especiall given the extra stress on your engine and catalytic converter that SammyK pointed out ? I say no.
 

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thanks for the excelet explanation. I have always used premium or mid grade in my Z3 and always wondered if I was wasting money. I am glad to know I am not!
 

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will-san said:
thanks for the excelet explanation. I have always used premium or mid grade in my Z3 and always wondered if I was wasting money. I am glad to know I am not!
I read in a car review from BMW source that it was "ok" that you go one grade down. The car can adjust for a drop in octane. What you will lose will be hp performance. The car just won't be as strong as the recommended octane. It won't hurt the car, but come on, if you wanted lower hp you would have bought a lower hp car.
 

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Fusionnv,
In my earlier post I did mention that you can run the engine on lower octane fuel,if the need arises, but it is not advisable to do so on a regular basis. If you read that post carefully you will also see the reason why ...that's the IC engine 101 course!
Now, I don't know what BMW source's rationale is for encouraging owners to run their cars on lower octane fuel. But if they actually said that then I would take everything they say with a healthy dose of salt.
Anyway, the damage caused by using one grade lower octane may not be immediately apparent. But doing so repeatedly, for long periods of time causes the engine to run on a richer fuel-air mixture. This, in turn, can cause an engine to “load up” when idling, foul the spark plugs, cause lack of power or make them run sluggish. The unburnt fuel that inevitably results will coat your catalytic converter, and reduce its efficacy. And all this is assuming that the engine computer can retard the spark plugs from firing and prevent knocking. Now, if this were me, I would rather not spend in the high hundreds to replace a catalytic converter (it has Platinum in it!).
Not to mention you will also see a drop in your mileage per gallon which will offset any reduction you will get in your gas bill.
Anyway, please read my earlier post again and try to understand the argument against using lower octane fuel in higher compression engines. Btw, note that having a higher horsepower engine does not necessarily mean that it uses high compression. I believe high octance fuels are required in engines where the fuel-air mixture's compression ratio is 10:1 or greater. You may have a 300 hp engine, but if the compression ratio is lower than 10:1, you don't really need premium fuel. Btw, your engine's compression ratio is probably listed somewhere on the owner's manual in the tech specs.
Cheers.
 

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Racadac3 said:
I have a 98 BMW 528 that I have always run with Texaco unleaded regular octane gas. I am intereted in purchasing a 2006 325 or 330 and was wondering if anyone is running anything less than the recommended fuel. I have a friend that has had several 740's and has always run them with regular gas.
I just pour in a mixture of 6 parts water and 1 part Dr. Pepper and it runs fine.

Please, do us a favor and buy a civic if you're too cheap to spring for an extra 5 bucks a tank at the pump.

Here is a very simple test a 4th grader could do to see if it's worth the price to use premium. It works on any car and was why I used premium in my Honda Accord.

Balance the cost of regular / the cost of premium versus the mileage on regular/mileage on premium.
 

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SammyK said:
Fusionnv,
In my earlier post I did mention that you can run the engine on lower octane fuel,if the need arises, but it is not advisable to do so on a regular basis. If you read that post carefully you will also see the reason why ...that's the IC engine 101 course!
Now, I don't know what BMW source's rationale is for encouraging owners to run their cars on lower octane fuel. But if they actually said that then I would take everything they say with a healthy dose of salt.
Anyway, the damage caused by using one grade lower octane may not be immediately apparent. But doing so repeatedly, for long periods of time causes the engine to run on a richer fuel-air mixture. This, in turn, can cause an engine to "load up" when idling, foul the spark plugs, and also lack power or run sluggish. The unburn fuel that inevitably results will coat your catalytic converter, and reduce its efficacy. And all this is assuming that the engine computer can retard the spark plugs from firing and prevent knocking. Now, if this were me, I would rather not spend in the high hundreds to replace a catalytic converter (it has Platinum in it!).
Not to mention you will also see a drop in your mileage per gallon which will offset any reduction you will get in your gas bill.
Anyway, please read my earlier post again and try to understand the argument against using lower octane fuel in higher compression engines. Btw, note that having a higher horsepower engine does not necessarily mean that it uses high compression. I believe high octance fuels are required in engines where the fuel-air mixture's compression ratio is 10:1 or greater. You may have a 300 hp engine, but if the compression ratio is lower than 10:1, you don't really need premium fuel. Btw, your engine's compression ratio is probably listed somewhere on the owner's manual in the tech specs.
Cheers.
http://www.usatoday.com/money/autos/reviews/healey/2005-05-12-bmw-3_x.htm

"How thirsty? Manual transmission models are rated 20 miles per gallon in town, 30 on the highway. Automatics are 21/29.

Trip computer in 330i automatic test car showed 24 mpg in 130 miles of spirited back-road driving. Trip computer in 325i test car showed 29 mpg in combination of 250 miles hilly highway driving and 100 miles of suburban run-around.

Premium fuel is specified; lower octane is OK but power drops, BMW says. "

Hey you should right a nasty letter to USA today and BMW NA. hehehe But I remember another article in the Times where they interviewed other car companies like Nissian, Honda, Ford etc. It basically came down to if you want you can use a lower octane as long as it doesn't ping. It won't hurt the car. You just won't be able to get the official performance numbers. It up to the owner if they wanted to save a couple of intial $$. In mileage or whatever i don't know.
 

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Well let me put it this way ...
If you want to design a bridge to handle 200 tons gross weight (of passing vehicles), you usually overdesign it and leave a safety margin ... so you would actually design it for 250 tons. So, an occassional load of 250 tons will probably not hurt it. But this bridge that was designed for 200 tons (expected), if operated at 250 tons load long enough, will result in stress fractures and other long-term structural damage. Thus, the bridge will last for 20 years instead of the originally intended 100-year lifetime.
If you are an engineer (and I am one), then you know what I'm talking about.
Now, I don't know what octane they designed these BMW IC engines for. Maybe they designed it for mid grade, and specify that users use premium grade to be on the safe side. So, quite likely, if the average owner (or lessor) operates the car for 6 yrs or less, you probably won't notice any significant ill-effects. But hey, if you want to run it on medium grade, then you can't very well complain if you need repairs after 6 yrs at 75,000 miles. (I am willing to bet that BMW will expect the engine to be out of warranty by the time such repairs are needed!) <evil grin>
hehe.
Your call! :D

Btw, the average user really does not notice pinging, even if it occurs, unless they are really in-tune with their car's engine noise. Mild pinging is not really noticeabe. For that reason alone, I would not count on being able to tell if that happens when using lower octane fuel.
 

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Did anyone else hear something about the possibility that lower octane fuel emissions could be harmful to the catalyst?

I was told that the higher sulfur contents of lower-grade fuel (In Canada) was not doing too well with the catalyst, but that was years ago and I had no source of confirmation.
 

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Lower octane is not the same as lower quality!
lower octane simply means that the Carbon chain is shorter. (Petrol is a hydrocarbon).
In most countries (including US/Canada), regardless of whether you buy Chevron or Exxon or Shell, the petrol is EXACTLY the same. The only difference in the brands is due to the detergent additives they add after the gas reaches the gas station. IMHO most detergents are almost the same. (For example, Chevron has the "Techron" branded detergent). So, if you think you are buying a cleaner (or better quality) fuel when you visit a Shell station, you are mistaken. And if you think that 91 octane fuel is any different in terms of sulphur content than 87 octane fuel, again you are mistaken.
There may be some exceptions to this, but most problems that occur when you fill at some problematic gas stations, is usually because of either intentional fuel adulteration or unintentional fuel contamination due to seepage of water and other mineral contaminants into the fuel storage tanks at gas stations and elsewhere. If there are any petrochem engineers on this forum, I'm sure they will let me know if I'm wrong!

re. fuels with high sulphur contents ..yes they do coat the catalyst. But here's an easy way to clean out the catalyst ....drive your car at highway speeds for an hour or two, and that should burn off most of the sulphur-based contaminants!
 
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