The engine is designed to run on 87. There's no point in running higher octane, unless you have a sketchy gas station with low quality fuel that doesn't truly meet advertised octane ratings, or if the higher octane fuels contain desirable additives that are not in the 87 fuel at your gas station.
The engine is tuned for 87 octane. Higher octane fuels burn slower and the stock tune of the 3.6 does does have the timing to take advantage of the slower burning fuels. With a tune that can take advantage of the slower fuel burn you will see an increase in HP and Torque. The gains are not huge but are real.
Can you cite any reliable sources of info to back this up?
According to the labels on the gas pumps, the displayed rating is the MINIMUM octane allowed for the fuel dispensed from that pump. There is no mention of +/- 2 variance allowed.
There is this misconception that running higher octane is better for an engine and will increase performance. This is only true IF the engine is designed to run on higher octane fuel.
And using higher octane fuel for the detergents isn't a valid reason anymore, since most lower octane fuels also contain detergents.
I have tried 87, 89, 91, 93, and 92 w/ no ethanol. The no ethanol 92 gave me the best gas mileage, and 87 the worst. The difference was minimal. I will run 89 most of the time and I run 92/93 if it is particularly hot out or I will be running the Jeep hard.
That difference can't be due to octane, or there's a reason (maybe carbon buildup causing predetonation, even if you can't hear it). A
Aside from something like that, if you run higher than necessary octane all you're doing is making the fuel detonate slightly later. And you computer will adjust the timing to compensate...there's literally no gain there.
Gasoline, however, has a higher energy content than ethanol, so 100% gas will give you better performance compared to e-10. Whether it's worth the extra cost at the pump is up to you. I don't bother in my Jeep, but my Corvette really doesn't like e-10. At all.
Try using the "Find" function under the "Edit" tab, <Control-F> on a Mac, in Adobe Reader to search the .pdf manual. I read your original post, opened my .pdf 2012 Owner's Manual, searched for "octane." Total time, maybe 10 seconds..... Here's a screen cap. the first hit: Several more hits confirm this recommendation.
I suppose the lesson here is that I should have asked for clarification of what RedBones meant by his statement of "It's plus or minus 2.". Sounds like we're arguing with each other based on completely incompatible assumptions of what RedBones was trying to say.
The compression on American engines is usually not high enough to require anything greater than 87 octane.
Import engines usually operate at higher compressions and almost all require 91 octane or greater. (I'm not sure why. I think it has to do with the type of readily available fuel overseas.)
There is absolutley no point in putting higher octane in a low compression engine.
But, putting lower octane in a high compression vehicle will not harm newer engines like it used to. The ecu will detect the increased volatility and retard the engine timing in order to prevent knocking.
As far as I understand, the ECU only retards timing to avoid knocking once it has detected that knocking is happening (knock sensor). It cannot analyze the fuel itself and predict that knocking will happen ahead of time. It's more of a safety net to limit damage from variations in fuel quality. I would not depend on it and intentionally use lower than recommended octane.
Mine started pinging on hot days once I put the 35's on it. I run 89 in the summer. I know these new engines retard the timing when they sense detonation, but its very noticeable when running with the doors off.
I have always preferred premium gas. Not any more. I tested my 2014 JKU with 91 for months. Average MPG with 91 was 15.79. Then I switched to 88/87 and it went up to 17.22 on average for three tanks full. I run nothing but 87 or 88 now.
Go with the octane rating that is specified in your owners manual. Those Chrysler engineers get paid big bucks to calculate such things. In the case of the Wrangler it specifies 87 octane.
Wow, reading through this thread was more entertaining than some of the oil change interval, 2 dr vs 4 dr, auto vs manual, etc., threads I've seen lately. Thanks, guys.
"Regular" in CO is 85 octane. The altitude allows a lower octane, but with my Wrangler, I've noticed that 87 or 91 both give better mileage, and I did a *lot* of experimentation and tracking to come to that conclusion. Almost all gas in CO is 10% ethanol, unless you get race fuel or E85 so I don't think ethanol content is the factor.
I've been getting my gas at Costco which only has two choices, 85 or 91. I've been going 85 one tank and 91 the next. If I get 85 octane, two tanks in a row, I definitely see a mileage drop.
YMMV.
To the guy who stated that "american cars" run regular and "foreign cars" need premium, let us know how that regular works for you in a V8 Mustang or Camaro. A Mustang 5.0 has 11.0:1 compression.
Give me a break. Don't put words in my mouth. I never said what you just put in quotes. Go back and read, I used the words like "almost" and "usually" for a reason.
The compression on American engines is usually not high enough to require anything greater than 87 octane.
Import engines usually operate at higher compressions and almost all require 91 octane or greater. (I'm not sure why. I think it has to do with the type of readily available fuel overseas.)
I think the domestic vs foreign statement was a generality, not a hard and fast rule. A lot of European cars and higher performance Asian imports do run higher compression than their American counterparts.
"Premium" is a marketing tactic to make people think higher octane is better. It kills me when people buy it just for the name. Whatever, it's their money.
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