6.6 Fuel Requirements

[JimBuck]

Question, does the 6.6 need premium fuel?  The 6.2 needed that.  Thanks,

[mkeddie]

No but I run it

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[TrailBoss1]

The 6.6 runs a fairly high compression ratio. Although it doesn’t require premium, and I believe the horsepower and torque ratings assume regular fuel, do you feel you get a benefit from the higher octane? Have you compared fuel mileage, throttle response, etc.? 

[Colossus]

What is the owners manual calling for? 

[JimBuck]

The owners manual talks about the 6.2 but not the 6.6 as far as i can see.

[ShotgunZ71]

I've run 87 since new, towing or otherwise. Running a higher octane may help when towing, but I can't say for sure. 

[redwngr]

OM says 87 for all gasoline engines except the 6.2 which it recommends 93.

Edited September 30, 2020 by redwngr

[Colossus]

You can try running premium a few tanks and see how she responds.  if you notice a good difference, feel free to stick with it, otherwise if it does just fine off of 87/89 go for it. 

[Stand By]

These are variable timing aren't they? The computer sets the timing and torque to your needs. I've run 87 for over 5000 miles without a hiccup. Including some heavier towing in hot weather. Dealer gave me the truck with a full tank and never advised to do anything special with it.

[Ray Pickle]

87 is what it is tuned to run on. I doubt computer will have parameters for higher octane in stock configuration. So far no aftermarket tuning options to take advantage of octane increase.

[greatmizzou]

Manual says 87, run 87

[Colossus]

The computer will adjust the timing somewhat depending on what you are running.  You might find better MPG and performance running on premium, or you might find it runs best on 89 or 87.  Try them a few times and decide for yourself. 

[Ray Pickle]

It won't take advantage of the octane rating near enough to cover the "25% premium" , premium costs. The fuel trim and timing windows are pretty tight in stock form.

[Dunn]

On 9/30/2020 at 3:21 PM, redwngr said:

OM says 87 for all gasoline engines except the 6.2 which it recommends 93.

thats what i read as well.......i ran 91 a few times couldnt tell a difference

Edited November 9, 2020 by Dunn

[webperson04]

I ran 87 for first 2000 miles and noticed 6-9 mpg towing and 10-14 mpg not towing. I switched to 91 octane premium and noticed significantly improved fuel economy (8-12 towing and 12-18mpg not towing. At a conservative 25% improvement, I'd say premium is worth it.