Gas mileage drop due to octane rating?

[Konradical6]

I have been running in 89 for a bit and getting a pretty decent 17mpg mostly city. Last two tanks we've put 93 in the car and now we are getting around 14mpg? Does that seem right?

2013 X5 35i 77k miles

[slovakE70]

Originally Posted by Konradical6

I have been running in 89 for a bit and getting a pretty decent 17mpg mostly city. Last two tanks we've put 93 in the car and now we are getting around 14mpg? Does that seem right?

2013 X5 35i 77k miles

I've never noticed increase in mpg when using higher octane on any car I ever had, simply because if car's not tuned for higher octane, difference will be minimal.
However, there's more things to consider when comparing fuel consumption, especially in city. Traffic density, driving style, air temp., idle time, number of cold starts etc.
And lastly, this increase in fuel consumption coud be indication that something with engine is not right, for example termostat getting bad, leaky injector, oxygen sensors getting bad etc..

[Thecastle]

Changing octane won't have a dramatic effect like that on fuel economy. Something else changed in your driving habits, weather, routes, and etc.

[NJX5D]

Buy a diesel
sorry just messing around. i need 4 replies before i can PM. Good luck w the question

[conmar]

Originally Posted by NJX5D

Buy a diesel
sorry just messing around. i need 4 replies before i can PM. Good luck w the question

Bad bad bad bad boy ...says a 40d driver
At topic:
First things I would check apart from changed driving habits,as mentioned before:
Last oil change
Filters
Tyre pressure

Just thinking ....fuel quality...unfortunately you do not always get what you pay for...