Fuel type on M50/E34 - 91 or 93 octanes?

[npmonteiro]

Hi guys,

I was advised to use premium fuel only on my 525i with an M50 engine in order to keep the VANOS engine in good shape. The fuel tank cap says 91 octane fuel only. The BP/Amoco gas station I regularly use has, besides the "regular (87 octane) fuel, both "silver" (91 octane) and "ultimate" (93 octane) fuel types. Which should I use?

Thanks for any and all guidance!

[5mall5nail5]

89 - 91

[russiankid]

I run 89 and have ran 87.

[npmonteiro]

So would 91 hurt the engine for having too many octanes?

[5mall5nail5]

You can never have too many octanes, only too few octanes.

[npmonteiro]

Thanks! Good to know.

[AZDinanE34]

Any gas is ok really but for a european sport motor like a "bmw" its good to use anything from 91 and up (USA). For purposes of burning properly in the motor and creating no sludge build up within the cylinders and other technical aspects. Thats why they say if you use 87 or any low quantity gas you should run 91+ every once and a while (like once a month) to help burn out the sludge and to help make your car run better.

here yah go:
http://en.wikipedia.org/wiki/Octane_rating

[sfgearhead]

Any gas is ok really but for a european sport motor like a "bmw" its good to use anything from 91 and up (USA). For purposes of burning properly in the motor and creating no sludge build up within the cylinders. Thats why they say if you use 87 or any low quantity gas you should run 91+ every once and a while (like once a month) to help burn out the sludge and to help make your car run better.

Octane has nothing to do with sludge buildup. Detergents keep your system clean, and most major brands will offer the same detergents in all grades of fuel.

Octane only refers to the fuels resistance to pre-detonation or pinging. A higher octane number isn't better, you're buying into the "if it's more expensive it must be better" philosophy. It's counter intuitive, but high octane actually burns more slowly than low octane.

In some cases running a higher octane fuel than necessary will cause the car to run worse than just running whats recommended. We had this problem when I was an engineer with Chrysler and spent a few weeks tuning the system so that the cars ran the same on any fuel. In most cases running 91 or 93 has no downside except to lighten your wallet faster.

I would run a known brand fuel, what ever the manufacturer recommends, which I believe is 89 AKI for our 1995 M50 (according to my gas door at least).

[russiankid]

Any gas is ok really but for a european sport motor like a "bmw" its good to use anything from 91 and up (USA). For purposes of burning properly in the motor and creating no sludge build up within the cylinders and other technical aspects. Thats why they say if you use 87 or any low quantity gas you should run 91+ every once and a while (like once a month) to help burn out the sludge and to help make your car run better.

here yah go:
http://en.wikipedia.org/wiki/Octane_rating

Don't baby the car thats all.

[TouringGuy]

I occasional switch between 87 and 91. I do notice a difference, nothing big but I feel the car is a lot quicker and responsive when using 91. Also my car gets better fuel economy. What is also probably effecting it is the times I get 91 I get 100% gasoline and no ethanol. I think 87 will do just fine but nothing wrong with getting the premium from time to time.

My car was saying I was getting 28 on the highway awhile ago, and around 20 in town.

[janders211]

Any gas is ok really but for a european sport motor like a "bmw" its good to use anything from 91 and up (USA). For purposes of burning properly in the motor and creating no sludge build up within the cylinders and other technical aspects. Thats why they say if you use 87 or any low quantity gas you should run 91+ every once and a while (like once a month) to help burn out the sludge and to help make your car run better.

here yah go:
http://en.wikipedia.org/wiki/Octane_rating
octane has nothing to do with sludge buildup.
Who are they?
What is a "european sport motor"?

[TouringGuy]

octane has nothing to do with sludge buildup.
Who are they?
What is a "european sport motor"?

they? maybe the Government? they out out a report saying that higher octane fuels do not increase performance etc.

[5mall5nail5]

Octane = sludge prevention

haha what? oh dear.

[russiankid]

Octane = sludge prevention

haha what? oh dear.
You didn't know that? You probably think running good quality oil prevents sludge don't you?

[5mall5nail5]

I don't run oil for that very reason

[russiankid]

I don't run oil for that very reason
Yeah see, you're with that group of people that think they know how to work on cars and how cars work. This thread will teach you a lot.

[5mall5nail5]

I know, I prefer to stay out of these threads to keep my street cred. No oil, no fuel, no problems. That's what I've always said!

[russiankid]

Go buy a wing.

[Kashmirbeige525]

http://www.hollow-hill.com/sabina/images/serious-cat.jpg