Octane question newbie

[dusterdave173]

OK New owner 2001 525 I Gas cap says 91 octane
PO says he never ran anything but regular--he never pushed or beat on the car
I have burned two tanks since purchase did not think about it and have been running regular--zero issues zero knock ping etc excellent running car
I am engine builder by trade and do muscle car engines so I am aware of the mechanics of this issue and the diff with alloy heads vs iron heads etc

Do you have to run more octane?

( for DD with wife driving) and maybe put in better when you want to beat on it?

Thanks

[dusterdave173]

New BMW guy here --scored a nice 525 I 2001 wagon filled it up and have put 500 miles on it used regular Then saw the 91 octane on the gas cap--called PO he says he runs regular so for wife DD is reg fuek OK?

[jclausen]

I go between regular and middle grade' I don't drive my car hard. Every Sunday I fill the tank which will be at half a tank so if I used regular at the last fill up I'll use middle grade the next time

[Pelican Parts]

I would say that you should use at least 89 octane - you'll likely get better mpgs than using 87. If you have a trusted indie shop, maybe reach out to them to get an opinion as well. Just my 2 cents...the E39 platform is excellent.

[dusterdave173]

Thanks!!! It is kind of like the trans service question --lots of different opinions so since I am a BMW rookie just checking--we do not plan on beating this thing at all --just a cruiser

[MIKYZZ4]

For use as a DD for your wife,regular is fine.
I will say I did notice a difference even in DD duty,
between regular and premium, but due to heat.

So my rule of thumb now is:
Summer(Memorial day - Labor day) = Premium only
Fall,Winter,Spring(rest of the year) = Regular

The basic difference between Regular & Premium is anti-knock compounds,
to prevent knocks and pings caused by high heat conditions.

[dusterdave173]

That sounds reasonable Thanks!!!!!

[cmoody]

That Touring looks great!

[dusterdave173]

We were THRILLED to snag it from PO old man drove it easy and kept it up--Inside is near mint--We are super happy so far

[gerry1000]

My understanding is that the recommended octane will yield better mileage and therefore offset some or all of the extra cost
Never tested this myself and not sure how much driving style has an impact