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)

[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.

[guinness]

Jet Fuel+Bimmer=Bad

[Nick.Hay]

I'm not sure if I want to know HOW you found that out!!

[Dash01]

FWIW, I've recently run both regular and premium in my chipped '90 535i: Seat of the pants, the car seems to run smoother and somewhat peppier with premium, and gets better fuel economy on the highway cruising at ~75-80 mph.

The better mileage pretty much offsets the higher price for premium fuel, so cost per mile works out about the same, with somewhat more pep.

[Jay 535i]

Keep in mind that different countries measure octane differently. An octane 'rating' of 91 isn't necessarily the same everywhere. You want to know how that number was arrived at.

[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