What octane of gas would you put in a 535i

[Puka]

Hey,

I've got a '91 535i 5-speed with only 19K miles (that's not a typo).
I've been putting 91 octane gas in it -- but would 87 or 89 be okay? What do you Americans put in the tank?

[guinness]

Do you have a proformance chip installed?

[Nick.Hay]

In australia, I use 'regular' unleaded, which is about 89RON I think.
I was told (by my mechanic) that using "Premium Unleaded" was a waste of money, as the engines are so refined, they don't need the extra octane.

Although I saw a 205L drum of "A1 Jet fuel" at my friend's farm... (Hmmm I always wondered why the John Deere sounds like a nascar)

[guinness]

Jet Fuel+Bimmer=Bad

[pundit]

...I was told (by my mechanic) that using "Premium Unleaded" was a waste of money, as the engines are so refined, they don't need the extra octane...

M30... refined??!! It may have been 30 years ago but by today's standards it is a low-compression, low-tech dinosaur. Hence it don't need premium! Fit an EAT chip (or similar) which increases ignition timing advance and you will then require higher octane, but not in standard trim. The later M50's, M60's etc have knock sensing and are designed for premium fuels.

[Paul in NZ]

i run 91 ron,and every now and then,96 or 98,ussually when going on longer trips,i get marginally better fuel consumption,it FEELS nicer and throttle response is just a little better

it says in the manual what the recomended octane rating for your market

[Randell]

my australian 535 has a sticker in the engine bay that says 'PREMIUM UNLEADED ONLY'. i take this seriously as i put in a tank of regular once and it didn't like it much at all

[Gayle]

Hey,

I've got a '91 535i 5-speed with only 19K miles (that's not a typo).
I've been putting 91 octane gas in it -- but would 87 or 89 be okay? What do you Americans put in the tank?

Got to ask the obvious. 19k? What's the deal?

Whatever you decide on octane, use a high detergent brand of gas. In the US, that would be Shell, and I think Mobil, and a few others. On my husbands high mileage e34, I noticed it immediately ran better when we switched to Shell. Switched after reading on this board that others had noticed their cars running more smoothly and having more power. Before switching, I thought gasoline was gasoline and why pay for an expensive brand. After switching, I understand that the price difference is the additives that keep you injectors clean and happy.

A couple of months later, we switched to premium in that car even though it wasn't chipped. We were having trouble with the CA emissions test, and Bill R advised us that a higher octane left less nitrous oxide cause of the temperature premium burns at. Higher octane made a big difference in how the car ran which really surprised me. Wasn't expecting it.

Run a couple of tank fulls of premium through your baby and see if she likes it.

[Derek A.]

Premium fuels have more detergents in them - which helps to keep injectors and intake valves free of muck. In the US BMW had a huge problem with "dirty" m30 motors - I think that is probably why the notion of using premium in an m30 came about.

[uscharalph]

Hey,

I've got a '91 535i 5-speed with only 19K miles (that's not a typo).
I've been putting 91 octane gas in it -- but would 87 or 89 be okay? What do you Americans put in the tank?

That's amazing 19k!!