For posterity's sake, here's what the TIS says:

"The knock control system carries out all knock-related corrections to the ignition timing and enables perfect operation also with regular grade fuel (minimum RON 91)."


(American regular is rated at (MON+RON)/2, and the RON of regular gas in most states is typically 91 or greater.)

My understanding is that the car auto corrects with timing if low octane causes knocking. I only know from my n=1 experience that I lost a ton of power but I'm a lead foot.

I know that I saw no difference with 89 non ethanol with the n55 motor. Mountain driving like it was stolen.

"Design of knock control system

The engine is equipped with a cylinder-row-selective, adaptive knock control system. A double knock sensor detects combustion knock. The sensor signals are evaluated in the DME control unit.
The knock sensor is a piezo-electric structure-borne noise microphone. It picks up the structure-borne noise and converts it into voltage signals.

Function of the knock control system

If knocking occurs, the ignition is retarded for a certain number of working cycles and then gradually approaches the original value. The retard setting can be controlled individually for each cylinder row (cylinder row selective).
In the event of the knock sensor failing, a fault code is entered in the fault code memory of the DME control unit. In the case of a fault, the engine is protected by constant retard setting of the ignition timing.

Installation Locations/Conditions

The double knock sensor is secured by means of an 8 mm screw on the water jacket of the engine block between both cylinder banks. It is arranged such that each sensor monitors one cylinder bank.
Only screw locking compound may be used to lock the screws. Washers, spring washers or serrated lock washers must under no circumstances be used."

What I don't understand is why you bought a BMW yet cheap out on something as simple as fuel? Saving $10 to use low grade fuel even if you are just going on a starbucks run makes zero sense. If $10 every fill up bothers you, you should buy a camry.

I never have... nor will I ever patronize a Starbucks. My coffee pot in the morning does just fine. :D Besides, by that position, owning a BMW at all is flushing money down the toilet when any number of less needy, more gas frugal, and cheaper alternatives exist. We all drive BMWs because we want to, not because we have to.

If some want to use regular... go for it. I just said, I'd never do it, and that $75/mo is a price I'm willing to pay to have the DME operate the engine at the optimum level it was designed. It'll pull timing if needed of course. I'm actually a fairly frugal person in most regards, much to my wife's dismay. :rofl:

And I certainly don't take the high and mighty elitest attitude x5Alpine does. He thinks if you change anything about a car to further your enjoyment of it you're a bad owner. God forbid someone want to make an offroader out of a BMW SAV or modify the audio system from the early 2000's... the horror.

I hope it doesn't cause permanent damage to your brain when you find out I only bought my E53 because it was the frugal option!!



I needed something that could tow my trailer and carry my family. A similar vintage 4Runner or Xterra with 200k miles at the time was fetching $15k. I bought my E53 for all of $6,300 in 2016 with only 93k miles, and despite spending a fair sum on preventative maintenance, I still have spent much less money on my Ultimate Drive-Thru Machine than I would have just buying a 20-year-old 4Runner, 4-door Tacoma/Tundra, etc. It's also much nicer than any of those cars. So I did indeed buy this car for the value proposition!


Again, TIS says the motor was designed to run on regular gas. That's the factory manual. I don't know what you think is so special about these motors that they deserve premium gas when the manual says to run regular.

not only does the manual say it but also the gas cap itself lol

Premium gas prices aren't so bad, viewed from a different perspective
 

I had a similar thought process (but from a different perspective), when I got my X5 Fuel prices at X5 fill-up time don't bother me much (the wife bitches, though), because the car it replaced used 117-118 octane race gas (about $22-25 per gallon) and got <5 mpg (as best I can remember...441 cubic inch engine, 1053 cfm carb, 4.88 rear gears, high stall converter). Whether the X5 gets as little as 15 mpg, while only doing super-short hops or driveway testing, it's still getting only Premium gas, at a fraction of the price.

I was considering returning it to street use, when my neighbor expressed interest in doing just that, so I proposed a swap of car-for-car, providing he buys and semi-restores one for me, off a short list of AWD/4WD SUV's. I may have lost a lot of money on the swap (the Chevelle was worth much more than the X5, for sure), but I wanted it to live again (after sitting in my garage for 13 years), and I'd always wanted

• 1) a 4-dr SUV, with AWD or 4WD, so I could tow my small trailer onto bad roads, when camping, and have enough space inside (the X5, not the trailer) for 4 or more people, when home,
• 2) a BMW (specifically an early X5...loved the design); always wanted a BMW, having nearly bought a '73? 2002 back in the day, but instead helped my brother out by giving him my (new)'72 VW SuperBeetle (leaving me only enough cash to buy another '73 VW SuperBeetle), so I never bought it

Besides, being retired, with no place to go (a respite from my former 30k miles a year commutes, and racing or camping excursions), I've only driven the X5 <1400 miles in the 2.5 years I've had it. With two pickups, my wife's car, and the ever-handy HHR Panel serving as grocery-getters & haulers, The X5 doesn't use much gas at all, so it's not a concern. Premium only.

91 ron (87 Octane) is the minimum.

It also says this, at least for the 4.8is:

The knock control provides:

- Protection against knocking damage also under unfavourable conditions
- High efficiency due to optimised use of the fuel quality and consideration of the relevant engine status
- Logistics advantages with regard to fuel availability
- Lower consumption and higher torque over the entire upper load range (corresponding to the fuel quality used).

So, by my understanding, and Andrew's experience, consumption or performance could be affected. :dunno:

This is an age old discussion regarding premium recommended vehicles. My thoughts, I wouldn't personally run less than recommended... but to each their own. The vehicle isn't going to blow up or anything.

I'd like to use cheaper gas if I can, although here in CA the difference between 87 and 91 is less than elsewhere. Don't worry, we more than make up for it.

From my 2001 X5 Owner's Manual, page 30.
"Fuel specifications
The engine uses lead-free gasoline only.
Required fuel:
> [B]Premium [/B]Unleaded Gasoline,
min. 91 AKI.
AKI = Anti Knock Index"

I've seen different Octane numbers before, but this AKI is new to me.

They did say "Premium" though.

The main concern I would have is if damage is occurring without me knowing it before it is too late. But for me, I'll keep using Premium, if only because I don't know better enough to use 87.

EDIT - quick google suggests the AKI is the same as USA Octane, so 91 AKI is true, Premium, mega-dollar, 91 Octane gas. I'm happy to be proven wrong.

this reference talks about how AKI fits with the more common ratings.

https://www.bmwmoa.org/news/438324/U...-RON-oh-my.htm