Call me a simpleton but if BMW recommends the use of premium fuel, it is doing so for a reason. If you can afford a BMW, you can afford the premium fuel.

 

ummm who are you referring too?

 

Now you're really going to get technical.

I will recite wikipedia
In some areas of the US such as the Rocky Mountains and other high altitude states, 85 AKI (anti-knock index) is the minimum octane, and 91 AKI is the maximum octane available in fuel. The reason for this is that in higher-altitude areas, a typical naturally-aspirated engine draws in less air mass per cycle due to the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill up a car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine due to knock.

 

Here is a word from your friendly BMW dealer:

http://www.imakenews.com/momentumbmw...KV0C1,bcC04dC9

 

I think a lot of us have missed the point of my original question. Answers like "just pay it", or "if you can afford a BMW, you can afford the gas" are appealing to the human need to oversimplify, but are beside the point entirely.

What I really want to know is if < 91 octane will cause damage to the motor. The reason I addressed it to the "gearheads" is because this HAS to be a technical answer.

From what I have been able to gather so far, it seems as though the E60 has been tuned for premium, therefore using less than 91 will increase the risk of pre-detonation under normal driving conditions. It seems as though if this happens even once, it could mean major damage to the motor unless the engine management is able to detect and PREVENT knocking. Anecdotal evidence seems to contradict the idea that the engine management system can only respond to knocking once it has already occured, because so many of us have used regular gas with no ill-effect.

Does anyone know exactly how the engine management system works to retard/advance the spark to avoid knocking? It seems as though the safety of using <91 hinges on the answer to this question...

(BTW, I only use top-tier, premium gas anyway, so this question is NOT about the price of gas. )

 

Simple answer? Read the article in the link above ^^^^^

 

I dont do that much motorways soI always use V power and nothing else.
I get more km from V power than the normal stuff, maybe it burns better
I can feel the difference in the 2.

 

You have answered your own question:

In normal driving regular will do just fine.

However, if you race from a stop light, floor the car every time you pass a car on a two lane highway (as suggested by another post) and want to ?wring out every last ounce? of performance out of your BMW, then use premium.

Again, the engine is tuned to achieve more performance from premium. But it will do no harm to run regular.

JeffK

 

ok how bout this. im not gear head but i will conduct my own MPG test for those who want to know. ive always wanted to know if the extra cost will result in better mileage. for the next 500 miles i will use 2 different grades (87 and 91) i get gas at the same place everytime so it will be easy. i will post my results using both premium and regular grade gas. first using premium then using regular for 250 miles each. ill record gallons comsumed over the 250 mile test for both grades. now i usually use 89 only because ive been told by many mechanics that only the top of the line highly tuned engines require 91 or 93 (if available). now we may think that out e60 have performance motors but lets be honest there are only a handful of vehicles that fall into the catagory of highly tuned machines. as for the original question regarding engine damage, i have no idea but at least this may help with some of the questions regarding mileage. wish me (and my engine) good luck

to be continued...

 

The long-term effect of using less than 91 octane is probably an engine with more stress (if tuned for 91 octane at normal altitudes), since it would have experienced more pre-detonation and knock events than if running on 91 octane or more. It can't be good for an engine for the fuel/air mix to pre-detonate under pressure or due to hot intake (summer) air while the piston is still in the compression / upward stroke. Retarding spark due to knock also means less power from same volume of air and fuel, so fuel economy is probably reduced as well. Probably not an issue for vehicles on leases.

BMW Service Centers have been know to collect fuel samples as part of certain engine diagnostics. I imagine the advanced engine management system probably logs the number or frequency of pre-detonation and knock events for diagnostic purposes. Therefore, warranty claims can be denied due to the incorrect fuel used.