Which grade of fuel can I use in my 300M?

Whatever grade the owner's manual says. If you use a lower grade than what the manual states, you will see a drop in performance and gas mileage. As strange as this may sound, if you use a higher grade than what the manual states, your gas mileage will drop, it will be harder to start, and idle will be rougher.

HTH Gyz

I use 87 octane and it runs fine. I'm pretty sure I've read this in the manual when I first purchased this fine vehicle :-) I have used 91 (midrange) on a couple of occasions but it didn't do anything for performance.

Come to think about it, I think I've seen more of the new 300s than I do of the older style ones?

I wonder where I can get this information from?

Ken