Sold on 89 Octane

[YBABRAT]

In this area, most gas stations have 87, 89, and 93 octanes. However, 89 is the least cost-effective grade to get. It seems to almost always be priced closer to 93 than it is to 87. So, if you need 89, the most cost-effective way to do it would be to fill half the tank with 87 and half with 93. You would end up with about 90 octane, and the price would be the net average price between the 87 and the 93, which around here is less than filling it with 89. .... But, I probably wouldn't do it that way if there was a line of people behind me waiting fo the pump. It does take a little more time, as you need to run the pump transaction twice.

Yeah, back in the day it served well... but never tried it with ethanol gas. No reason to, until my curiosity got me. Ever since ethanol became forced upon us. Gas milage suffered with the cars I had. There was a time after 9/11 few had ethanol in my state. By 2015, you had to look for pure gas. Like every other station would have it. Now it's rare to see it.

The local station here Pure has 93 octane no ethanol
Another station out of town has 87 octane no ethanol.

I looked up my state for verification of pure gas locations.... here is the site. pure-gas.org

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[roaniecowpony]

...

Far as I know, the 3.6's are designed to run on 87 (full power). They might quiet down a little bit with some higher octane but it doesn't seem to provide much more power like engines designed to run it.

That's the spec in the manual. But it also says " While operating on gasoline with an octane number of 87, hearing a light knocking sound from the engine is not a cause for concern." . Well, it is to me. These engines seem to have a problem with head gaskets leaking. Knocking, even light knocking raises the cylinder pressures above normal. Knocking under heavy load can put the engine outside the design parameters pretty quickly.

I'm not interested in either more power nor more fuel economy. All I care about is keeping the engine out of any knocking. Ever.

 

[TheRaven]

I'm not interested in either more power nor more fuel economy. All I care about is keeping the engine out of any knocking. Ever.

Your engine will knock on 93 octane too...you just won't hear it. That said, I don't hear any knocking from mine on 87.

There seems to be a lot of misunderstanding on this forum about how modern electronic engine management systems work.

 

[SaintNick]

I've ran 91 no ethanol top tier fuel since new.

Now that I'm back in Utah I run non ethanol 88. I get better mpg by quite a bot here in Utah. Driving conditions are definitely different and obviously the weather with no humidity.

 

[AFD]

One thing about automatic gear selection. It will shift into 5th and 6th just to get into the 3000RPM band. Even though a higher gear would drop down to save fuel. In the long run bumping up to 70MPH and keeping steady does save fuel more than babying through 6th and 7th gear at 60 or 65MPH.

Yeah, I never understood how a vehicle with angle/orientation sensors, that knows damn well you're going up a steep hill, still allows the auto trans to upshift and keep the RPMs low when downshifting or keeping the same gear would allow you to pull the hill better and more efficiently.

Feels like I'm always mashing the throttle and trying to get a faster running start, so by the time I'm nearing the apex the auto trans slows me down to my normal speed. When shifting manually, this really isn't a problem and it's much easier to maintain a constant speed on long inclines.

And as far as octane, ever since I saw both a Jeep factory technician and a well-regarded Pentastar tuner here both recommending at least 89 for the newer, high-compression 3.6L, I've been sticking with that. Fuel economy seemed to improve a few ticks, but could've been from several other variables (less ethanol, tire wear/pressure, condition of air filter). Engine longevity is far more important that fuel economy or increased performance (if tuned for the octane increase).

 

[veryfewposts]

Now that I'm back in Utah I run non ethanol 88. I get better mpg by quite a bot here in Utah. Driving conditions are definitely different and obviously the weather with no humidity.

Interesting. In higher elevations than even yours, I found I'm lucky to get 1/2 MPG bump running 87 no ethanol. Compared to 85 octane with ethanol blend. In multiple studies from multiple vendors.

I "feel" like the no ethanol gas is better qualitatively, and I feel better using it or blending half/half, but my MPG numbers have never been there, in any season. 3.6.

 

[Maverick909]

I ran 87 for the first couple months with my 3.6. Couldn’t stand the knocking jumped to 91 Oct and it’s been quite ever since. I’ll run 91 until it’s gone. I’ve always ran 91 in my 5.7 hemi ram after it below the engine running 87/89 oct that the book said to run. Only lasted 44k miles on the lower grade fuel. Put another hard 100k miles running 91/93oct and the thing purred like a kitten

 

[pablo_max3045]

Seems cheaper in the long run to just run the gas specified by the manufacturer rather than lower grade fuel.
Assuming the worst case and it breaks your engine; assuming a 65 cent difference in the price per gallon and an average of 23mpg, you could save enough to pay for a new engine (assuming 13k USD), but you would have to drive for about 460k miles to get a wash on the price of the engine.

 

[YBABRAT]

Seems cheaper in the long run to just run the gas specified by the manufacturer rather than lower grade fuel.
Assuming the worst case and it breaks your engine; assuming a 65 cent difference in the price per gallon and an average of 23mpg, you could save enough to pay for a new engine (assuming 13k USD), but you would have to drive for about 460k miles to get a wash on the price of the engine.

Like the old fram commercial.... you can pay me now or pay me more later.

If it were not for the peppy 3.6L and it's wanting to fly attitude, I could live with 87 octane. But, flat land operation is nothing like mountain operation. I'd rather treat my baby right than have it become a sick dog. Morning starts since running VA 87 never sounded as good with 89.

As for fuel economy... i attribute it to Pedal Monster. I had to lower all I could to make my throttle less touchy and have a nicer linear feel. The out come was just that, and fuel economy showed that a higher squirt was being done by ecu to counter ping with regilar gas under load. The hotter the burn and hotter the engine, pinging will happen easier with 87 even if richness of fuel mixture is maxed out. Though on high elevation a rich burn is less efficient as it requires more air to properly burn. No amount of octane boost will correct it.

The pedal monster should benefit mountain use more than flat lander use. But I like it for everyday use no matter where I am driving. Without it all I saw at best was 20.4 MPG, and that was in rare occasion. Approaching 26MPG was with pedal monster and 89 octane.

When I need another fill up, I will try pure gas 87 with pure gas 93 50/50 mix.

The only other time I saw a result in power with a small bump in fuel economy in playing with a factory fixed rich burn without a tune, was with my Honda. I added a MDX spacer kit to raise the factory intake manifold 2 inches. It basically lengthened the intake runners to allow more torque. I could get around 34 MPG out of a v6 auto when an i4 could get 40 MPG with a 6 spd. I could not have achieved it without a torque gain. Still ran rich bit that was part of the factory going with regular gas instead of premium. One thing that keeps me away from turbo engines is premium gas. Yes you can run on regular but it's not the same as premium when things stabilize from changing to premium.

 

[Kyanche]

I used to use 87 in my Jeep with the 3.6 and decided to try out 91 last year. Since then I've stuck with the 91, but I've got to say: I've seen no difference in gas mileage, power, or "smoothness". In fact earlier today I noted that it still makes that sound like ice and rocks in a blender when I cold start it LOL.

 

[1BadManVan]

We live at sea level, I always run 91 in our 3.6, definitely runs much smoother after initially running 87 when we first got it. Smoother powerband, better mileage and no audible pinging. Wife wants to keep it until the wheels fall off, so I would like to keep the engine as healthy as possible

 

[YBABRAT]

I used to use 87 in my Jeep with the 3.6 and decided to try out 91 last year. Since then I've stuck with the 91, but I've got to say: I've seen no difference in gas mileage, power, or "smoothness". In fact earlier today I noted that it still makes that sound like ice and rocks in a blender when I cold start it LOL.

Maybe those who pay for 89 and premium gas get the placebo effect driving?

 

[alphawolff]

Your engine will knock on 93 octane too...you just won't hear it. That said, I don't hear any knocking from mine on 87.

There seems to be a lot of misunderstanding on this forum about how modern electronic engine management systems work.

The engine needs 89 octane. It will, however, run on 87 by retarding the timing. 90% of owners will never notice this. I can tell when accelerating hard during a hot day immediately the engine is retarding timing based on experience. Again, most people aren't in-tune to this and do not notice it. The best description I can give it is the engine is running on marbles instead of air. You can physically feel the difference.

87 was fine for the older 3.6L with its lower compression. They didn't raise the octane for the new 3.6L because of emission and fleet requirements, even though they really should've. Even the 2.0L, which 100% needs premium, can and will run fine on 87 by retarding timing and sacrificing power and fuel economy. I do not believe you'll see much if any fuel economy differences in the 3.6L, but the difference in power is especially noticeable on hot days.

 

[YBABRAT]

The engine needs 89 octane. It will, however, run on 87 by retarding the timing. 90% of owners will never notice this. I can tell when accelerating hard during a hot day immediately the engine is retarding timing based on experience. Again, most people aren't in-tune to this and do not notice it. The best description I can give it is the engine is running on marbles instead of air. You can physically feel the difference.

87 was fine for the older 3.6L with its lower compression. They didn't raise the octane for the new 3.6L because of emission and fleet requirements, even though they really should've. Even the 2.0L, which 100% needs premium, can and will run fine on 87 by retarding timing and sacrificing power and fuel economy. I do not believe you'll see much if any fuel economy differences in the 3.6L, but the difference in power is especially noticeable on hot days.

Seems like TheRaven's remark sort of contradicts it's self. You explain better than just making a remark.

Makes me wonder is he talking about his own understanding?

 

[roaniecowpony]

I don't drive much since retiring. Last four years, I probably averaged about 5-6k a year on the jeep. That may go up in the next year. But if you said I drove 10k miles in a year, and I got 14 mpg (37s and either trails or town driving) over the year, thats 714 gal, and I pay .40 more for 91, that's $285/year. If I blow a head gasket, you do the math on how many years of driving with the cheaper grade it would take to break even.

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