High octane gas, why?

[DuaneD]

What creates the need for high octane gas? Is it all related to the compression or are there other factors involved. Do all BMWs need high octane? What about a 1992 535i?

[KC Ron Carter]

That is new and unmodified.

The issues are the carbon buildup and changes to the ECU maps installed by the owners.

Carbon buildup can be fixed by using monthly a container of
ChevRON TechRON. The ChevRON TechRON is to clean the back side or tulip of the valve
and all components on the fuel path, of varnish.


You can also use the steam clean once a month.
It is a manufacture provided service procedure to flash the combustion chamber with steam to force the carbon to break free from the piston face and valve face.

With the engine at normal operating temperature and approximately 2000 RPM, allow the engine to ingest by a vacuum hose 12 oz soda can of water.

A puff of steam and the carbon is gone.

Later,

[Tile19]

It's true carbon build-up is easier to get from lower octane but the compression ratio denotes the octane. If you use lower than recommended octane you will cause detonation in the engine cylinders, this will cause excessive wear and result in eventual power loss and a noisey engine. The proper octane level or higher will provide a cooler burn in the engine making your catylitic components last longer. hope this answers your ??

[buymeabmwm3]

agree with tile19, octane is a measure of knock resistence. personally though i think bmw is kind of childish about saying it needs premium fuel. i think it just says that because bmw is a luxury brand, and it serves to maintain the image of high-classery. higher octane fuels also tend to have more detergents and additives that prolong engine life, so it may also be bmw's way of saying "here, this will protect your car so it lives longer than those dirty gas guzzling domestics."
for some comfort, i have actually run my car on a tank of 87 with no problems. turns out the guy who pumps gas at the station put in 87 instead of 93 like i told him. (yeah new jersery doesnt let you pump your own gas, costing me a full afternoon of trying to siphon my tank, and sressing about blowing the head off my engine, which wouldnt have been an issue if i could just pump my own freakin gas). Plus I have a conforti engine chip, which changes your fuel and ignition maps so you really REALLY need to use premium, for real, or the engine may knock. Well, no knocking ever happened. so i dont think its anywhere near as big an issue as people make it up to be. basically, if you hear your engine knocking, you need a higher octane (esp a prob in the summer). i wouldnt stress about switching off with tanks of 89 or 87.

[wbaneham]

BMW engines use knock sensors which will retard ignition when you use low octane fuel, so the overall performnace of the engine suffers usually.
Premium is used in higher compression, high performance engines, as higher octane fuel burns at a slower rate of ignition, allowing for a combination of ignition advance and high compression, which means more power is produced.

[LBOCEAN]

Pitching in here...

What's the difference between octaines, such as 87 to 89, other than 10 cents per gallon (more or less)?

It's an additive the gas companies add to every 100,000 gallons of gas, mearly to kickup the octain to...89%

Does it do any good.... No. It takes more out of your budget, but does nothing for your car.

It's the same pitch you get about changing your oil every 3000 miles. Bottom line is you don't! Changing your oil every 7-10,000 is perfectly fine.

A test performed back in the mid 80's, on NY City cabs proved that no one paticular oil broke down under typical use by the 3000 mark. They continued running the vehicles with the same oil and found that the typical breakdown of most oils was between 7-10k. (Most around 10k)

Back to Octaine...

Bottom line here is if your car is anything less than 250 HP, use 87 octaine.

Using a higher octaine other than whats suggested for your vehicle actually causes more carbon build-up and leads to symptoms of rough idle, poor gas milage and power.

Preventitive Maintenance;

What more can I say.... "A Must"

If your not comfortable working on a car yourself, most dealerships will perform an EFI for around $100. Local automotive centers can be $25-$45 less.

A minor investment for keep your vehicle running good.

[MioCLK]

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
http://www.chevron.com/prodserv/fuel...i_octane.shtml

[csieminski]

To answer one of the original questions in this post, I do not believe that the 3.5/3.4L engines in any BMW 5-, 6-, or 7-Series require premium fuel. According to BMW, regular can be used. However, the smaller 6-cylinders (the 2.5L and 2.7L like in the 528e I had) require at least 91 octane. I assume this has to do with a higher vs. lower compression ratio. So a 1992 535i should be fine with regular, even by BMW.

[LBOCEAN]

Originally Posted by csieminski

To answer one of the original questions in this post, I do not believe that the 3.5/3.4L engines in any BMW 5-, 6-, or 7-Series require premium fuel. According to BMW, regular can be used. However, the smaller 6-cylinders (the 2.5L and 2.7L like in the 528e I had) require at least 91 octane. I assume this has to do with a higher vs. lower compression ratio. So a 1992 535i should be fine with regular, even by BMW.

When you say By BMW, does that mean you've gotten straight from the horses mouth? (in a matter of speaking)

[csieminski]

Put it this way--an acquaintence let me ride in/drive his '89 535i Automatic a couple years ago. I was leafing through the owner's manual in the glovebox, which listed specs, including octane requirements, for both 525i and 535i that year. I'd take information provided in the owner's manual somewhat seriously. If you're really concerned (and I'd want accurate information myself if I was unsure), you could contact BMW corporate or a dealership.