Octane

[Hd74ica]

Hello,
Sold my '18 2500 6.4 and bought a new 2021 2500 6.4 with a 3.73 4x4 and have a question regarding octane. I know my 18 owners manual said mid grade 89 was preferred however the 21 owners manual says nothing about mid grade 89 and states to use 87 (without ethanol). So I'm looking for input from the board regarding 87. Also will the 3.73 get better MPG than the 4.10 I had? Thanks for the info.

David
Michigan's thumb

 

[Ricktara]

I have a 19 with 3.73. I use 87 with no issues.
I think the mileage is unmeasurable between the 2

 

[HEMIMANN]

That's odd, seeing how most of USA is forced to use only ethanol blended gasoline. I haven't seen indications that Gen V Ram trucks did anything to Gen III Hemi engines?

In fact, the Corn Lobby was trying to get EPA to force 15% ethanol blend down our throats until the Engine Manufacturer's Association (EMA) balked and said they woudln't warrant engines anymore. That brinksmanship finally got the lobbyists to back down to the current 10% maximum ethanol.

Maybe a Hemi engine designer will weigh in here, cause corporate won't say anything, as we've seen multiple times.

 

[Firebird]

I always ran 89, because I towed a lot

 

[Hd74ica]

I miss stated, the manual says "Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine." My confusion is nowhere can I find 89 octane is recommended as it was in my 2018. Thanks.

 

[HEMIMANN]

I miss stated, the manual says "Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine." My confusion is nowhere can I find 89 octane is recommended as it was in my 2018. Thanks.

OK, that's better! *phew*

The fuel system is not designed with components to handle the solvency of high alcohol content, is what this means. That hasn't changed at all.

There's a bunch of threads in here on octane. It'll run fine on 87, but it is designed to make use of 89 by sensing knock limits and advancing ignition timing to the burn rate of 89 octane. You get more power and better gas mileage with the 89 octane. Yes, you pay more but it maximizes towing torque.

We have regular, midgrade, and premium octane gasoline around here. Many engines require higher octane now, as they use smaller, high compression ratio, and turbocharged engines to get higher fuel efficiency. Have you googled for mid grade gas nearest your zip code?

 

[Hd74ica]

All the stations here have mid grade which is 87.

 

[retired]

2020 6.4 and I have run all 3 ie 87,89 and 91 and no difference in mpg or how it runs. I just use 87 most of the time now.

 

[Dean2]

I have a 2021 6.4 with 3.73. The first 1500 Klms I ran it on 91. The next 1500 on 87. So far I am actually getting better mileage with the 87, last tank of highway driving was 18 mpg, but that could also be the engine breaking in better. I will re-test with 91 Octane to see if it is the gas or break in. I know the 2020 Grande Cherokee with the 5.7 gets better gas mileage by almost 15% on 91 Octane when the temp is above 80F. Below that 87 and 91 give the same gas mileage, and that is over 22,000 Klms of testing the two different Octane levels. (I hand calculate all mileage figures. The Jeep EVIC is within 1/2 mpg most times, usually on the optimistic side. So far the truck has been within 1mpg, but it is 50/50 as to whether it is reading too high or too low.)

If you run the same tests on your truck and diligently record mileage, driving conditions, temperature etc, you will soon find out if the Octane makes a difference in your type of driving. At Costco, Regular 87 Octane gas here is 4.60 Canadian for a U.S. gallon. Premium 91 Octane is 5.04 so if you aren't getting better mileage for the extra 13 bucks a fill there really isn't a good reason to use the more expensive option. (Stations other than Costco 87 is 4.96, 89 is 5.92, and91 Octane is 6.20, so at that difference of 19% and 25% or 30 bucks a fill, 89 and 91 would never make sense.)

 

[2012RAM1500RT]

When gas was .10 cent difference between 87, 89, 93 I would argue with you all day about difference in power and MPG but costing as much as .70 cent and $15 more a tank just for 20 gallon I would not buy 91 or 93 for more MPG or power. In my vehicle it's impossible to justify it for either power or fuel mileage. I have a 87 octane tune on my tuner through Hemifever and couldn't be happier. Now if I was going to race it on the track I'll spend the extra. Just my opinion!

 

[Riccochet]

Seems they change the owners manual every year. My 2020 manual says to run 89.

 

[Scottly]

The fuel system is not designed with components to handle the solvency of high alcohol content, is what this means. That hasn't changed at all.

There's a bunch of threads in here on octane. It'll run fine on 87, but it is designed to make use of 89 by sensing knock limits and advancing ignition timing to the burn rate of 89 octane. You get more power and better gas mileage with the 89 octane. Yes, you pay more but it maximizes towing torque.

How do I give 20 likes to a gasoline thread where a guy knows WTF he's saying??

 

[Hd74ica]

Dam, I mean mid grade here is 89. Guess I'm having a senior moment. Bawhahaa

 

[retired]

Seems they change the owners manual every year. My 2020 manual says to run 89.

my 2020 manual says 87.
FUEL REQUIREMENTS — GAS ENGINE
6.4L ENGINE
Do not use E-85 flex fuel or ethanol blends greater
than 15% in this engine.
This engine is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high quality
unleaded gasoline having a posted octane number range of 87 as specified by the (R+M)/2 method.
While operating on gasoline with an octane number of 87, hearing a light knocking sound from the engine is not a cause for concern. However, if the engine is heard making a heavy knocking sound, see dealer immediately. Use of gasoline with an octane number lower than 87 can cause engine failure and may void or not be covered by the New Vehicle Limited Warranty.

 

[ramffml]

The computer will detect knock and retard timing on 87. Your truck will run, but it's still knocking; the computer reacts only after it detects the knock, the knock happens first.

And maybe some of you elderly gentleman simply are unable to hear the difference at this point, but I sure as heck can; sounds like marbles rattling in a glass can (softly/faintly, but its there if you know what to listen for and the windows are up, music off, kids mouths all duct taped up, climate control off etc).

It really doesn't matter what the manual says. Quoting the manual is very much missing the point. What the truck says is king; and my truck says: run 89 or 91 if you can.

 

[2012RAM1500RT]

I hate and will not tolerate any spark knock what so ever. If the computer is smart enough and fast enough to prevent mine from spark knocking at all I'm fine with that. I know what spark knock sounds like (been a mechanic for 45+ years). I run 89 the majority of the time because the manual says so but I also will try 87 sometimes to see if I can tell the difference and in mine it is so small mileage wise and power wise I will not argue it. I will tell you if the difference was so noticeable I would spend the extra for 93 or any other octane, it's not about the money, it's what I get in return for the money.

 

[retired]

I know exactly what pinging is and mine does not do it on 87. I suppose depends on where you buy your fuel and where you live. live out west and buy your fuel at Cenex and you won't have an issue.

 

[Riccochet]

my 2020 manual says 87.
FUEL REQUIREMENTS — GAS ENGINE
6.4L ENGINE
Do not use E-85 flex fuel or ethanol blends greater
than 15% in this engine.
This engine is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high quality
unleaded gasoline having a posted octane number range of 87 as specified by the (R+M)/2 method.
While operating on gasoline with an octane number of 87, hearing a light knocking sound from the engine is not a cause for concern. However, if the engine is heard making a heavy knocking sound, see dealer immediately. Use of gasoline with an octane number lower than 87 can cause engine failure and may void or not be covered by the New Vehicle Limited Warranty.

That's FCA's way of saying "you can run 87, and it won't void your warranty, but it's going to pull timing, and thus cut power, to keep the engine from destroying itself."

 

[PCT]

That's FCA's way of saying "you can run 87, and it won't void your warranty, but it's going to pull timing, and thus cut power, to keep the engine from destroying itself."

i have ran 87 for about 20,000 miles and havent noticed jack. i ran 89 from about 1000-1500 miles and noticed 0 difference in all aspects.

 

[ramffml]

These engines are built at the same spec; if my truck pings on 87, so does yours. It's really that simple.

If you say "my truck doesn't ping", I promise if you wire up an obd2 data logger and look at the results, you will see it there in black and white.

Your truck most certainly pings on 87, doesn't matter what quality of gas you use. It's the low octane that is the problem.