I'm not really answering your question but I always used 93 octane. Some people use 87 or 89. It's an arguement for the ages.

 

I've run my '93 on both standard & premium unleaded. Didn't notice a difference really. I would guess milage is a bit better on premium but nothing in my manuals suggests you have to use premium. Perhaps just fill up every 3rd or 4th time with premium as it's got more cleaning agents which could help keep things clear.

 

I live in Kansas, and octane levels are lower here. Regular Unleaded is 87, Midgrade is 90, and Premium is only 91. Midgrade is basically premium fuel, but only a couple cents more expensive than regular, so maybe midgrade wouldn't be a bad choice.

 

I guess the best way to find the answer. Is to look up what the AKI "anti knock index" on a KL-03 2.5L .

 

Know where I might find that?

 

I use to know, but I've forgotten it.

 

We measure our octane rating differently Downunder but I always notice improved performace, economy & smoothness with higher octane fuels.

 

If you want, read this article I posted last year in Ford World Wide News. It might answer some questions. http://www.fordforums.com/showthread.php?t=45176&highlight=octane