Just curious to what octane everyone is using in their 3.6 JK

 

I have a big issue with ethanol. I try to run 89 or 93 with out ethanol when possible. Finding pure gas isn't easy though. I get a little more economy out of my 3.6 with the higher octane fuel.

I also put a can of Seafoam in the tank at each oil change, and let that do it's magic. That helps counter some of the water build up and keeps things clean.

The only other thing I do fuel wise is I make sure and run the gas all the way out, like, fill up when the fuel light comes on. If you're never going to let your gas get too low, you're good. But if you put 50-60K on your jeep, and never let it get below 1/4 tank, then all the sudden run it empty, you're asking for trouble. Water build up, gunk and crap will be settled at the bottom of the tank, and it will be too much for the engine to cycle. If you're running it out every time, there won't be enough debris and water built up to cause any problems, and the engine "eats" it with out issue. You just have to decide how you want to do it.

 

85
More mpg out of a higher octane is bogus. Higher octane is more stable, that's it. Doesn't burn cleaner, doesn't improve mpg, etc., etc.

I've been running regular 85 or 87 depending on altitude, since new and no issues whatsoever.

 

87 here.

 

I always burn "regular" grade gas in all my vehicles.

In my younger days when I drove more hi-performance cars I debated what grade of fuel to run. Higher grades of fuel did perform better but, for me, the increase cost did not appear to be worth the extra coin spent to fill my tank. So, I did a performance test with each grade and found that for my driving the more expensive fuel was just that- more expensive. During my experimenting I discovered that if the vehicle would knock or ping with the lower grades of fuel It was because it was not tuned to run on the lower octane. I further discovered that when I filled a tank with lower octane fuel then towards the end of that tank tuned the engine for the lower grade fuel, the engine was happy and did not complain. The key was to tune the engine for the "lower" grade fuel once all of the higher octane was purged from the tank. In all cars that I did this test (including my '55 Chevy and '70 Dodge Challenger with the magnum engine) I found this to be the case.

KG6SLC aka Eugene

 

I run 87. I'd run 85 if they sold it here.

Octane rating has absolutely nothing to do with the mileage you will get. It is NOT an indicator of the energy contained in the fuel. It is a measure of how resistant the fuel is to combustion due to compression.

If you run 87 and are not getting any knocking, there is no benefit to running a higher octane rated fuel. The user manual even recommends against using premium fuel.

Ethanol does contain less energy than gasoline, so mileage would be higher with pure non-ethanol gas than the 10% Ethanol gas sold almost everywhere these days.

 

Interesting. I can't say I share your what i'm assuming to be personal experience. I am a fuel mileage lunatic. I clock every tank and do the math manually. I always have with all my vehicles. One thing I've noticed over the years is a sudden fall off in MPG's to be a sign something isn't working right or needs cleaned. I've consistently noted better marks with higher octane fuel. This is especially true for me with vehicles that I've had, that had performance modifications. Since driving style is situation based, to be accurate, it takes a lot of data to be able to make an accurate assessment.

My last modified vehicle was a Silverado with custom exhaust, long tubes, Powerbond balancer, performance tune, etc... Even before the mods, that 5.3 preferred the higher octane fuel, and after mods and tune, it would spark knock with out higher octane fuel. I don't remember if I posted pictures of the build or not, but some of my write ups on that last build can be found at: PerformanceTrucks.net Forums - Powered by vBulletin When I make mods, I dyno it.

 

You'll get better mileage with 100% gasoline, but I haven't ever observed it with different octanes.

 

Compression ratio is what drives the need for higher octane fuels. My Corvette demands 97 and so does my Tacoma with a TRD supercharger, both have hi compression motors and will ping from using the less stable lower octane fuels. My Jeep does not. There is no more BTU's in high octane fuel so I just cannot see getting more gas mileage form higher octane fuel. Don't waste hard to come by cash on higher price fuels in your Jeep...My 2cents

 

87 if it runs good with it. I run 89 most if the time because I get some detonation or spark knock on 87. I live in FL and temps are usually high and I tow a 19' boat. While 87 does fine in the winter, the engine knocks when temps are above 80 especially when towing.