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Discussion Starter · #1 ·
Same stretch of road (45 miles), same direction, same weather, almost empty tank before each fill... ZERO difference between regular gas and premium as far as what average was reported by the computer. Test done in 40F weather
Test done in 40F degree weather.
 

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:appl::Thanx:
 

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Discussion Starter · #3 ·
Only weird thing i noticed was that on the mostly downhill first half of the trip the regular gas got better mileage, while on the hillier second half, the premium closed in the gap.
I know all about octane, preignition and why premium shouldnt be better in cars that dont need it, but i find it interesting that when you push the 3.6 harder, it seems to maybe like premium more. Could be useful to people that tow with their JKs, otherwise I'm pretty convinced it's just a waste of money under most conditions
 

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I would not expect a difference...slightly less if you were really killing it, perhaps.

Premium isn't better by default...
 

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Discussion Starter · #5 ·
DJL2 said:
I would not expect a difference...slightly less if you were really killing it, perhaps.

Premium isn't better by default...
Well, there have been people on here that have claimed their JKs run better on premium, and there's also the argument that no ethanol (premium in canada has 0%) would lead to better economy (which it does, but since the 3.6 isnt able to use the higher octane, it shows no difference due to the wasted unburned fuel going out the exhaust).
I just wanted to prove it for myself, when I accidentally bought unmarked premium from a gas station (had no idea what marked fuel was until i went to pay). The sales clerk didnt care, and did confirm that it was just 91 with a dye in it and it wont mess anything up
 

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In early September I ran a 3 tankful test of the non-ethanol premium in my own 08JK.

Over mostly same roads/route/speeds etc in the same part of the county.

Mostly low density traffic areas where I usually average about 19.5 anyway. I live rural setting and tend to avoid city congestion as much as possible. Sometime I tow a Bantam with various loads. I made one 200 mile round trip on the freeway. I expected to find at least .5 mpg improvement.

This fuel load cost IIRC about 50 cents extra per gallon, meaning about $6 extra per fill up, about 250-300 miles. I recorded no significant difference in either calculated or on-board ECO read out.

I noticed no difference in performance. Disappointed I returned to regular corn power.

I considered trying the aviation grade 100+ octane gas for comparison. Haven't yet.
 

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I still don't understand how there could be pre-ignition on a EFI motor that has knock retard sensors..

My dad would use regular fuel in his 1964 Galaxie 500 when traveling North on I5... and premium fuel (Ethyl) when traveling up mountain roads while towing the tent trailer.

He always told me using premium gas for traveling on a flat road was a waste of money.

I guess his theory still holds true to this day...

.
 

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I considered trying the aviation grade 100+ octane gas for comparison. Haven't yet.
At $6.73 a gallon, don't bother.

When I was into Harley Davidson, we did tests with 100 octane avgas in high compression modded engines and stock engines. Other than being needed to prevent engine knock in 110* F desert heat in the 12.5:1 mill, all it did was run up the balance on the gas credit card.
 

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Good thread! Thanks for the info, I've been wasting money on premium with the thought I was babying my high mileage YJ but it sounds like I'm just throwing money out the window
 

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Discussion Starter · #10 ·
m998dna said:
I still don't understand how there could be pre-ignition on a EFI motor that has knock retard sensors..

My dad would use regular fuel in his 1964 Galaxie 500 when traveling North on I5... and premium fuel (Ethyl) when traveling up mountain roads while towing the tent trailer.

He always told me using premium gas for traveling on a flat road was a waste of money.

I guess his theory still holds true to this day...

.
There can be benefits to runing a higher grade fuel on EFI car, in really hot temperatures! The fact that the engine is really hot, increases the chance of pinging and ignition retard, so a medium grade could restore lost power felt, by allowing the engine to advance timing again... Not sure how that would affect fuel consumption though
 

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I considered trying the aviation grade 100+ octane gas for comparison. Haven't yet.
That would be a serious mistake. Avgas is always in my experience a leaded fuel. Aside from the EPA kind of issues I suspect you might do some damage and certainly run the risk of voiding your warranty.

Avgas is also rated on a different octane scale than mogas (used to know the difference but now plagued by CRS). The biggest reasons for avgas being so much more expensive are the relatively low production quantities, higher quality assurance measures (if bad gas blows up your car engine, the maximum liability is probably the cost of the car), and need for better vapor pressure characteristics to deal with the higher altitudes that an airplane may reach.
 

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Most of the recent generation high performance V6s on the market require 93 octane or higher. The Pentastar is the only one I'm aware of that calls for 87 octane or higher. Hmmm... Is that indicating to us that Jeep is holding back the Pentastar's capability in order to make fuel ups more convenient?
 

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Most of the recent generation high performance V6s on the market require 93 octane or higher. The Pentastar is the only one I'm aware of that calls for 87 octane or higher. Hmmm... Is that indicating to us that Jeep is holding back the Pentastar's capability in order to make fuel ups more convenient?
My 2012 Lexus also has a 87 minimum requirement, it's all in the ECU.
 

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Discussion Starter · #15 ·
WXman said:
Most of the recent generation high performance V6s on the market require 93 octane or higher. The Pentastar is the only one I'm aware of that calls for 87 octane or higher. Hmmm... Is that indicating to us that Jeep is holding back the Pentastar's capability in order to make fuel ups more convenient?
If they are high performance V6s, they probably have high compression ratios, so it would make sense to run higher octane
 

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Had to fill up w/ Premium (93) no-name gas during the fuel shortage after Hurricane Sandy and noticed no difference whatsoever from running Regular (87) tier-1 gas.
 

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Most of the recent generation high performance V6s on the market require 93 octane or higher. The Pentastar is the only one I'm aware of that calls for 87 octane or higher. Hmmm... Is that indicating to us that Jeep is holding back the Pentastar's capability in order to make fuel ups more convenient?
93? .... I haven't seen 93 octane (normal retail gas) in California since the 70's or 80's.

However, I ran 76 Union unleaded 100 octane in my 1965 Plymouth. That stuff cost $6.00 per gallon when gas prices were cheap. There's only a few gas stations that carry it in SoCal.

Nobody runs Avgas.. maybe in the old days when you couldn't find racing gas...

.
 

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"Nobody runs Avgas.. maybe in the old days when you couldn't find racing gas..."

Thanks for the various comments gents....

jiggling the few remaining little gray cells.....my last experience WAS with an old hot-rodding buddy who continued to build his big-bore high output monsters until just after the y2k business....

He developed cardiac issue and died short of his 60th birthday.....

Tribute: his last project was a 46 Hudson pickup with IIRC 454-hogged out, normal carburation, ran the 1/4 mile at 98+mpg with the weeks groceries in the bed....HE'S the one that ran av-gas with no catalytic issues.....

so I won't be lapsing into that error on my 3.8 Jeep....

thanks for the discussion
 

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There can be benefits to runing a higher grade fuel on EFI car, in really hot temperatures! The fact that the engine is really hot, increases the chance of pinging and ignition retard, so a medium grade could restore lost power felt, by allowing the engine to advance timing again... Not sure how that would affect fuel consumption though
Back in the 90+ degree heat of last summer, my 3.6L would commonly ping even under normal acceleration. A tank of mid grade now and then cured it. Now that the cooler weather is here, I run regular and no pinging.
 

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I accidentally put 87 in my bike because I got use to putting it in the Jeep. That made my bike run like crap.
 
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