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The octane specification for the 500 is 87 minimum, 91 recommended. Around here, the typical choices are 87, 89, and 93. I've been using 87. Occasionally, when hot, the car will idle a little rough, but that's the only issue I have and I suppose it might be helped with higher octane fuel. It would cost me another 50 cents per gallon to go to 93. What do other people run?
 

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92-93 octane. It's only 20 cents difference here. I plan on weighing the fuel econ difference between 87 and high test.
 

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I intend to go midgrade and probably once a month I think I will toss in some octane booster made by Lucas, then some fuel treatment as well to keep things inside tidy.

Octane Booster:

Fuel Treatment:

That's enough booster for 1 year and enough cleaner for 100 gallons.

I see no reason to run 93 octane when the midgrade (89) and 93 in tests I read before rated them so close and with 87 being somewhat poor for mileage and a clean burn I intend to avoid it altogether.
 

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I used 87 on the first two tanks and got combined 32 MPG. Third tank I moved up to 89 with little or no change in MPG. Last tank went to 93 which cost me 30 cent more per gallon and now averaging 35.7 MPG. With it only costing me $3.00 per tank more and the car running smoother and getting better gas milage I am going to stick to 93.
 

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I've only been filling up with 91oct in California. seems to be peppy for what it is. I haven't been driving in sport mode but I was testing it out last night after refueling and it seems to have an added kick, although it's not mentioned for 5MTs.
 

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Hi

Fortunately near me (in Northern Virginia), the local Sunoco station serves 87, 89, 91, and 93 octane fuel. Unfortunately not all other stations around here do so. So I usually try and go to the same station (when I can) to make sure I can get the 91 octane fuel.

The few times that I went to a station that didn't have 91 octane, I think I used 93 instead.

Regards

Pat
 

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Well only filled up once but I decided to go with 93 for awhile, I think I am going to be averaging around 31 MPG since I run with the AC blasting pretty much 99% of the time, hopefully when summer ends I'll jump a few MPG. I am concerned the MPG and overall running of the engine might suffer if I drop to 87 so I still think 91 is ideal.
 

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The Owners Manual recommends 91 octane or higher. Don't offer 91 in my area so I use 93. Moving from 87 to 93 definitely improved my MPG. Went from 32.3 to 35.7 so I will stick with the 93. Cost 30 cents a gallon more which equates to about $3.00 per tank. Seems worth it to me.
 

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I know premium fuel does a lot better at high altitudes. I use 91 octane...
The car has less power at higher altitude because the air is thinner. The car will be pumping less fuel into the cylinders to compensate for the lesser amount of air. Unless these cars compensate for altitude by leaving the valves open longer.

I have never even seen anything higher than 91 octane when I am in Colorado.

I use 93 Octane here. I do notice a little better mileage on the 93, not sure if it is enough to wash the cost difference. $3 more for tank of 93 is the same as roughly 1 gallon or 40 miles on 87.
 
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