Regular vs. premium for an '03 MINI Cooper


i’ve been using regular for several years now. have sacrificed some mpgs. is this b/c the fuel mix is less rich? i do all the commonsensical things one has to do to save fuel: drive slower, watch the braking, use AC less often, etc etc.

please enlighten, you experts out there!


The reason your engine has lost MPG is that it is running in a less than optimal manner. Its retarding the timing in an effort to reduce/stop damaging pinging since regular fuel is more volatile than premium. I would check and see if the $0.20/gallon “savings” is balanced and likely negated by your MPG loss. Beyond the MPG loss you get a power loss also.


The one important thing I can’t answer is to be found in your owner’s manual Does it recommend premium or does it require premium. If it says premium is required than you are chancing engine damage by continuing to use lower octane fuel. I might suggest that the A/C thing is a rather small effect and may even be reverse on some cars at highway speeds.


An engine that normally runs on regular gas will see no improvement using premium, but one that is supposed to burn premium (yours) will yield a decline in performance if it burns regular gas. Apparently you can use either grade. The sensors are able to determine which fuel is currently in use and will adjust engine timing accordingly.

So you may continue to fuel up with regular grade gasoline. As you said, you will sacrifice a few mpgs and therefore must pay for more fuel than if you had used premium. You can do your own math to determine if there are any actual dollar savings. If it were my car I would use only the grade recommended by the manufacturer.