Premium Unleaded?
 

Do I have to use premium unleaded in my '05 X5 or can I use regular unleaded?

I think the minimum you can use is 91... I think people HAVE used lower octane ratings, but I don't think it's good.

None of the BMWs I've owned have ever run properly on anything but premium.

All BMW's are optimized for high octane (premium) gas, that includes the sotware (the chip) that runs your car. Putting lower octane in your car won't break it, but your car wil not run as well, and you could void the warranty. Also keep in mind that you won't save money on gas as well since your overall milage will go down as well... Cheaper gas= Lower milage (if your car is optimized for higher one, of course).

There is some discussion In This Thread as to whether lower octane gas is good or bad for the X5.

Actually the octane level does not effect gas mileage. Additionally, your engine management software will adjust detonation for the lower octane level.

"Additionally, your engine management software will adjust detonation for the lower octane level."


If that is the case then why bother stating in the manual to use min 91?

Because that is what the software is optimized for from the factory... It will adjust though. Pre engine management software cars would not be able to adjust and you would get knocking in the engine because the detonation wasn't executing correctly.. Modern cars adjust... It would be better of course to use the 91 octane - but of course with what gas prices are...

I see. Thanks for the explanation...makes sense I guess. But can you tell me why it would be better to use the 91 :dunno:

Here is a quote from an article about gas

What's the benefit of higher octane?

Higher octane fuel has only one beneficial feature - it allows an engine to run at higher temperatures with more advanced ignition timing under higher levels of compression witout detonating / knocking. Higher octane fuel does NOT have more potential energy and will not make an engine perform better unless that engine is knocking. On modern engines with knock sensors, higher octane fuel may make the engine run better if the knock sensors are retarding the ignition timing, which hinders performance. High octane fuel does not burn cleaner, it does not clean your engine, it does not increase horsepower or torque (unless you are experiencing knock), it does not smell better, it does not increase fuel economy (unless you are experiencing knock) and is not better for the environment. If you buy higher octane fuels for any of the above reasons, STOP!

here is a link to the article

http://www.superchargersonline.com/content.asp?ID=105