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85 octane gas in Cmax?


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In a number of states, mostly NV, UT and CO, only 85 and 91 octane is available. So far I have been going with 3 gallons of 91 and 10 gallons of 85 to kind of get 86-87, but it's annoying. Can I just use straight 85? I mean, everyone pretty much uses 85 in those states and I have not heard of any issues so far.

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Basically I don't know for sure but it may be fine.

 

"The most typically used engine management systems found in automobiles today have a knock sensor that monitors if knock is being produced by the fuel being used. In modern computer controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level"

 

http://en.wikipedia.org/wiki/Octane_rating

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Most of the stations I recall in Utah had a mid-grade, that was around 87 octane -- though not all stations will have it. The reason for the 85 octane is because running a slightly lower octane, at high altitudes, compensates for the thinner air. You'll likely be fine running the 85 octane but, since 87 is recommended even at altitude, you might use the GasBuddy app or website (or similar) to find stations that sell mid grade gasoline in your area.

Edited by raadsel
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I experimented with this during our road trip. The car adjusts the spark based on octane & air entering the engine. You can find my observations about how the car behaves with different octanes of fuel and while at different elevations in this thread: http://fordfusionhybridforum.com/topic/9689-road-trip-observations-with-torque-pro/

 

Unfortunately from my iPhone I can't figure out how to link to a specific post for you. But the octane observations are on pages 1 & 2 I think.

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In a number of states, mostly NV, UT and CO, only 85 and 91 octane is available. So far I have been going with 3 gallons of 91 and 10 gallons of 85 to kind of get 86-87, but it's annoying. Can I just use straight 85? I mean, everyone pretty much uses 85 in those states and I have not heard of any issues so far.

In those states I use the mid grade. In NM it is around 89 as I recall. I also get better MPG at high altitudes.

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Well, there is this note in the owner's manual:

 

Octane Recommendations
Regular unleaded gasoline with a pump (R+M)/2 octane rating of 87 is recommended. Some fuel stations offer fuels posted as regular with an octane rating below 87, particularly in high altitude areas. Fuels  with octane levels below 87 are not recommended.

 

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