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Gas Octane
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.
| | Reply » Gas Octane |
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
| | Reply » Gas Octane |
Hey there...  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.
| | Reply » Gas Octane |
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.
| | Reply » Gas Octane |
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.
| | Reply » Gas Octane |
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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Gas Octane