What octane of fuel do you run with the 7.3l?

Locally, the cost difference between 87 and 91 is typically 10-20 cents. Today it’s $4.65 for 87 and $4.85 for 91 at my preferred station (after local rewards.)

I fill up every other week, or 26 times a year on average. Meaning the average potential cost saving of using 87 over 91 every time for me is ~$133/year.

Since Ford recommends 91 for “best overall performance“, and I tow a lot, and am in hot weather a lot, the potential cost saving of using 87 some of the time for regular duty doesn’t offset the cognitive overhead of forecasting my use case or need for “best overall performance.”

I would re-evaluate that if the local price delta was more like the 0.80c/gal that it is for some of you. Or if I routinely refueled multiple times per week. Or if I didn’t use the truck at all in harsh conditions or for towing.

Quite a spread of potential impacts here. Great thread.
 
Interestingly enough, If I continue to just fill up at costco and blend half regular 85 with half 91, I'll end up with 88 octane gas that's still 20-50c cheaper per gal than the local midgrade 87 at current prices.
 
I think the RFI for y’all is whether or not that ECU will adapt to premium fuel, adjusting the timing accordingly. That would yield (marginally) increased performance and clean up any potential for gunking things up. The way the manual suggests this is the case.

This was an interesting read.

Last summer I towed our 10k travel trailer from Washington state to Cape Cod, down to the Maryland shore, back out to Yellowstone NP, and back to Washington. 8000 miles in 6 weeks.

Along the way I experimented with all sorts of fuel. 87 ethanol, 92 ethanol, 91 non-ethanol, 87 non-ethanol.... you get the picture. Filling the truck twice per day some days gave me a lot of miles to experiment. It was summer, so the heat we encountered while towing suggested (according to Ford) that I should be running higher octane. I did notice better mpg with higher octane non-ethanol, but the difference wasn't much. In moderate summer weather I ran 89 octane and in hot conditions 91 or 92, non-ethanol when I could get it. It was my perception (again, no scientific data here) that the lack of ethanol made more of a difference than the octane, but I like the idea of giving the motor a more consistent and controllable fuel burn with the higher octane when towing and running the motor at high RPM's.

Take that for what you will. I usually fill my truck at Costco when it hits half a tank, and alternate between 87 and 91 each fill, keep it in that 89 range. I ran 87 exclusively for the first year I had the truck and I'm sure its fine, but I don't always know when I'm going to be towing a boat or a camper so I keep a little higher octane in the tank.
 
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Has anyone tried the 87 octane but ethanol free? Here 87 with ethanol is 1.66$ per gallon vs ethanol free 87 at 2.12$ per gallon. Supposedly better mileage with ethanol free, less corrosion issues.
These prices didn't age well... lol

I read this and was like holy shit where do you live, then looked at the post timestamp
 

Meh, I’ll stick with 85 octane & not worry about it

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I've been putting premium 91 (in CO) almost exclusively. The last tank was 87 non-ethanol just to see if it was any different (was the same price as premium). I did put E85 in once because I used to use it exclusively in my 5.0 F-150, but that was tuned. I won't do that again.

I just wish all of the pumps didn't shut off after $100...
 
I run 89 in my 5.7 Grand Cherokee.

I'll mostly run 89 in the Tremor. When I'm towing my adventure house on wheels, I'll will bump that up to 91(If i hit the Sunoco by my house) or 93 at most any other station.
 
I run 93. I do not put a lot of miles on so the cost is not a factor for me. But I do know most engine management systems can read the octane of the fuel in the vehicle and can either advance or retard timing. With the advance in timing there should be more horsepower. I am not a technician but have been told this.
 
I have been using the Maverick 88 octane non-ethanol stuff 85% of the time. I hadn't noticed the manual recommended 91+ until today. I don't know what's "better" 88 non-ethanol or a corny 91... Anyway, when I'm driving highway (empty) I get 14.5 mpg or so.
 
I run 93. I do not put a lot of miles on so the cost is not a factor for me. But I do know most engine management systems can read the octane of the fuel in the vehicle and can either advance or retard timing. With the advance in timing there should be more horsepower. I am not a technician but have been told this.
You are correct.
 
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