I know you can use 87 or 89, and I've done a search but the only threads I seem to be coming up with are for 2nd and 3rd Gen.

What grade are you guys using? I have used nothing but 89 since I got my truck but I was recently talking to a couple 4th Gen owners who have used both and they have found they get much better mileage with 87. Anyone else found this?

I am thinking about switching if theres much truth to it. How will this affect my engine? My last car...before my first Ram I used 94 for almost a year after purchasing and then dropped down to using 89 when gas prices hit record highs here. Manual said 89 and above was all good for that car but I got alot of engine noise....ticking etc. I switched back to the 94 and almost all the noise was eliminated by about halfway through the tank of premium gas. Would rather deal with the increased cost rather than deal with any annoying noise.

Any insight would be helpful. Thanks

 

We took a trip down to Tennessee to see some family. Ended up being 1600 miles round trip. On the way down we used only 89 octane and got 18.2 mpg. While we were there we used 87 octane to "flush" out the system and then used 87 octane all the way home and got 18 mpg. That is all hand calculated. I did not see any significant difference in mileage so I am sticking with 89 octane since it is around 8 to 10 cents cheaper than 87 octane here.

 

I've tried 87 on a couple tanks, 89 on a couple tanks, got slightly better MPG with the 89. I did the math for the additional MPG vs 10 cents more per gallon for the 89, its almost break even, so I'll stick with the 87 octane.

 

I ran a couple tanks of 89 and noticed no milage difference so I've been sticking with 87

 

i have used 87, 89, 91, and 93.. i have noticed better mileage with 87.. and i get no engine noise. if i ever hear a knock or a ping i will go back up but for now i'm running 87...

 

I've been running 87 octane for the last couple months. Previously used only 89. Mileage seems a little less. But that could because of winter blend fuel and more time idling. Anyway not a big difference. What I did notice is much worse mileage when I pulled a 5000 lbs. trailer. So if I know I'm going to be pulling I'll switch back to 89 to try and confirm this belief.
But I'm pretty sure anything over 89 octane would just be a waste of money.
So I guess I would say between 87 & 89 use whatever fits your budget.

 

last few fill ups were 87 octane.

 

Bought my truck in March and used 89 almost exclusively the first 4-5 months. Switched to 87 due to fuel prices and used only 87 since. I have noticed about a 0.5 mpg increase with 87 but this could be a false return because the switch occurred about at about 6-7k miles. Generally this is when engines start getting better mpg due to engine break-in so take this result with a grain of salt.

As too performance, i have towed a 3k lbs trailer with no adverse affects using 87. However I have noticed a fairly significant difference in power between 87 and 89. Except for HP/Torque rating my truck runs no different from 87 to 89.

On a side note, people often make the mistake of putting higher octane than the manufacturer suggests expecting to get more power. This is a misnomer. Stock vehicles are tuned (compression, valve timing, etc.) to take advantage of a certain octane rating. Some vehicles, such as ours, can be optimized for multiple octane ratings due to mechanisms such as variable valve timing. So using gas with octane ratings in excess of factory recommendations is just a waste of money. I speaking strictly of gasoline, not other fuels like ethanol as ethanol burns hotter and therefore produces more power. This however is a different mechanism completely unrelated to octane rating. Any one with conflicting beliefs please post as i always enjoy a good debate. (Its a good way to learn something new.)

 

My 09 4X4 1500 ram 5.7 also does a bit better with the 87 I think. I took a 275 mi trip east and got about 16.7 with 87 in it, on the way back I got 15.9 with 89 in it. Both ways speed was about 75+...Not sure but there might of been slight a head wind comming back.

A quick note on gasoline.. Gas has about 114500 BTU's per gallon regardless of octane rating. Ethanol has about 76,100 to 81,800 BTU's per 1.5 gallons

Octane is only related to the stability of the burn....The more stable burn = the more timing that can be introduced which means higher cylinder pressure = more HP

A gallon of gasoline has the same amount of energy in it at ANY octane rating.

 

It's only a theory and based on personal assumptions from the way these PCM controlled engines behave but here goes:

These PCM's sense everything in their environment but astrological alignments and I believe that they (at least on the Dodges I've owned) adapt to the fuel grade to provide peak HP/Torque with the following caveats:

1. Protection of the mechanical components of the engine/transmission overrides all other performance objectives.

2. Fuel economy (MPG) is the second priority in order to meet fleet economy mandates. (except for WOT performance)

3. Driveability (smooth, comfortable and quiet) factors come third.

All that being said I think that under normal weights/loads the lowest octane recommended for the vehicle provides the best bang for the buck.

When towing or hauling weights above 50% of the GCVWR, the higher octanes enhance both the performance and economy primarily because the PCM senses that it does not have to "protect" the engine from detonation to the extent it would with a lower octane. For me, the 20% additional cost of higher octane fuel is warranted for the "driveability" and peak torque attained.