87 octane vs 89 octane, fuel economy differences

[Firebird]

I have been running 89 octane since day 1 in my 2023 6.4, and my average economy in town is 12.5 hand calculated. After reading on here about folks using 87 octane, I decided to switch over to see if any difference. Well, after running 87 for 3 tanks, my hand calculated economy has dropped to 11mpg. Same gas stations, same roads, same speeds. I will switch back to 89 now. Truck has 3300 miles on it.

 

[Grateful Dad]

I ran nothing but 89 in my ‘21 but decided to give 87 a go with the ‘24. Only thru the first tank so didn’t calculate that one yet but it looks like I’m getting maybe 11.5

Truck only has a smidge over 400 miles on it so it’s a bit early.

 

[Pitboss44]

That’s pretty much exactly the mpg difference I got between 87 and 89 but it’s $0.50 more for 89 here. So $3.09(87)/ $3.59(89)=11/12.5 mpg it works out to something stupid like .7 miles per dollar more cost effective to run 87

 

[Firebird]

Fortunately, mid grade is $3.09 here

 

[Hunter11]

I have run both in my truck several times and have seen no difference in mileage or performance. I now run 87 but always Top Tier.

 

[Crusty old shellback]

No need to waste money on high octane fuels. These are not high compression engines, so they do not require the higher octane.

Lots of factors come into play for the MPG, so saying you got worse by switching to a lower octane is not really accurate.
Sart/stops. Acceleration differences. Different roads. Different temps, different amount of idle time, etc will make a difference.
Now if you did this in a controlled environment with controlled fuels, then the results could be acepted.

I've used the same fuel on the same roads and vary from 11 to 14 MPG. It all depends on throttle, speed and idle time.

Engine masters on YouTube has a video where they tested different octane fuels on the same OEM style motor. No difference in HP/TQ to mention.

 

[Rockcrawlindude]

when I bought my 2019 it recommended 89 in the manual. Around 2020 they updated the manual and those trucks recommended 87. I didn’t know that until spending some time on this forum, about two years into my ownership, and I never switched off of 89.

 

[Crusty old shellback]

Not sure why they woukd say 89. These engines are not 13:1 compression or higher.

The higher the octane, the higher heat it takes to denote. Also the slower the fuel burns.

 

[Firebird]

All I know is same roads, same stations, same city, same temps + or - 5° and worse economy on 87

 

[Enve46]

I’ve been running 93 in my mine, it’s what I ran in my 2016. My driving is all city and stop and go, maybe 5-10% hwy and I’m at 9mpg which I don’t really mind. But I doubt a change in octane will yield any results but I’ll try 89.

 

[Crusty old shellback]

All I know is same roads, same stations, same city, same temps + or - 5° and worse economy on 87

I'm not saying you didn't see a difference in MPG, but there are other factors.
Did they both have the same amount of ethanol? Same blend? Winter blend vs summer blend.
Same oxygenated or not?

 

[whitexc]

I’ve been running 93 in my mine, it’s what I ran in my 2016. My driving is all city and stop and go, maybe 5-10% hwy and I’m at 9mpg which I don’t really mind. But I doubt a change in octane will yield any results but I’ll try 89.

My daily (turbo Subaru) takes 93. Not a chance this pig of a truck is getting that treatment!


Sent from me

 

[sanda]

Testing fuel mileage on my 2014 2500 and now 2021 2500 both with the 6.4
I tow heavy about 10K miles per year.
In Colorado our low grade octane is 85.
I experiment with different octanes, 85-93, and have never been able to tell any difference in power or mpg's . This is towing over high mountain passes as well as the deserts of Arizona.
Believe me if there was a noticeable difference I would buy the more expensive octanes.

 

[Crusty old shellback]

Here's some antidotal edivince for you. Not that it really means anything. Not trying to be a A hole, just showing you how everything matters when doing comparison test.
Last year I made 2- 550 mile trip from Ventura, CA to Reno, NV.
Same route, same gas stations, same speeds, etc. Big difference was on the second trip, I was towing a small Uhaul enclosed trailer loaded up.
On the second trip, you would think my gas milage would be worse.
Nope. I got 2 MPG more with the trailer than without

I spent the last 25 years doing Test and Evaluation for the Navy. One thing I learned that to compare apples to apples, everything has to be controlled and the same. If they are not, then you have to note the differences and take them into account to determine the differences in the results.

So to say you went with a lower octane and got worse milage, but not take into account all the variables at play, then really means nothing.

 

[Firebird]

I'm not saying you didn't see a difference in MPG, but there are other factors.
Did they both have the same amount of ethanol? Same blend? Winter blend vs summer blend.
Same oxygenated or not?

Yes on ethanol, blend, same station
we have been on winter blend since September

 

[Enve46]

My daily (turbo Subaru) takes 93. Not a chance this pig of a truck is getting that treatment!


Sent from me

I hear you. I drive with a heavy foot and want everything it has, that’s my theory at least. I’ll try 89 but don’t think I’ll go to 87

 

[gimmie11s]

All I know is same roads, same stations, same city, same temps + or - 5° and worse economy on 87

This is not surprising. Horsepower requires x amount of ingnition timing. It takes MORE fuel to achieve that ECU-commanded timing when fuel octane is low. Theoretically (depending on the timing ceiling), the truck should use less fuel if the octane rating is higher.

You should now try and run some 91 or 93 octane and see how that compares to your 89 octane MPG.

I'd imagine 89 octane is where the timing map on these trucks is centered around -- meaning you won't gain anything MPG-wise going to 91 or 93, but you'll lose MPG going to 87.

The language in the owner's manuals seem to support this theory.

 

[Rockcrawlindude]

This is not surprising. Horsepower requires x amount of ingnition timing. It takes MORE fuel to achieve that ECU-commanded timing when fuel octane is low. Theoretically (depending on the timing ceiling), the truck should use less fuel if the octane rating is higher.

You should now try and run some 91 or 93 octane and see how that compares to your 89 octane MPG.

I'd imagine 89 octane is where the timing map on these trucks is centered around -- meaning you won't gain anything MPG-wise going to 91 or 93, but you'll lose MPG going to 87.

The language in the owner's manuals seem to support this theory.

This makes sense.

 

[JustARam22]

Crazy how the gas trucks get the same or worse then diesel

 

[Grey]

Look at the bright side, every 250 miles or so you can change if you didnt like the last choice.