87 vs 86 Octane?

Tumbleweed

Tumbleweed

Member
I'm heading to EJS next week. Trailering the Jeep. 2011 JK. Here in Michigan 87 Octane is Regular. I understand that in Moab it might be 86? I usually fill up before my trips, but was wondering if I should. Will there be any real difference between the 2 octanes at the higher elevations of Utah?

Thanks for the help.
 
OverlanderJK

OverlanderJK

Resident Smartass
Tumbleweed said:
I'm heading to EJS next week. Trailering the Jeep. 2011 JK. Here in Michigan 87 Octane is Regular. I understand that in Moab it might be 86? I usually fill up before my trips, but was wondering if I should. Will there be any real difference between the 2 octanes at the higher elevations of Utah?

Thanks for the help.
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I think when I was out in Utah a couple weeks back they had 86, 88 and 90. I used 88 since I'd rather go up then down. But it's not every gads station that's like that.
 
olram30

olram30

Not That Kind of Engineer
Is 85 too low? Would that cause engine knock? Just curious, I usually put either 85 if I'm broke, and 87 on pay day
 

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13_gecko_rubi

13_gecko_rubi

Caught the Bug
The higher octane is just to prevent preignition, ie knock. The higher the altitude the lower the air density so you need less octane since you won't get knock. You are essentially lowering the compression as you go up in altitude due to less air. If you have a supercharger don't go lower. Without one, 85 is fine. Even if you get knock, your engine has sensors and will back off timing to prevent it. Not good for long term but short term that's what it's for. The issue is if you fill up in Moab and don't burn it all out then go back home where you need it, no bueno. For the extra $0.10/gallon just use 87.
 
olram30

olram30

Not That Kind of Engineer
Oh. Will I guess I better stick to 87. I also live around 7000 feet elevation.
 
jelliott076

jelliott076

New member
olram30 said:
Oh. Will I guess I better stick to 87. I also live around 7000 feet elevation.
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Run 85 or 87 octane for a year then pull your spark plugs to see all the garbage left behind. You'll find it rather shocking. Then do the same test with 91. The mileage you'll get out of it is much better and it doesn't leave as much trash behind.
 
Zstairlessone

Zstairlessone

New member
13_gecko_rubi said:
The higher octane is just to prevent preignition, ie knock. The higher the altitude the lower the air density so you need less octane since you won't get knock. You are essentially lowering the compression as you go up in altitude due to less air. If you have a supercharger don't go lower. Without one, 85 is fine. Even if you get knock, your engine has sensors and will back off timing to prevent it. Not good for long term but short term that's what it's for. The issue is if you fill up in Moab and don't burn it all out then go back home where you need it, no bueno. For the extra $0.10/gallon just use 87.
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But up there 85 costs the same (or more) as 87 down here. At least in western Colorado it did so that 87 or 88 is even more than that.
 
Remlap

Remlap

New member
Dug up this thread searching about Octane.

Please tell me if I'm just getting a Placebo effect here, but when I was up Camping near Rico CO last month all they had was 86 Octane which I filled with a couple times.

On the way home to AZ through the Flagstaff mountains we got a flashing engine light when hitting near 5K RPM (downshifting uphill), it did this a couple times down here too heading back up the mountains at high RPM's only.

No code was stored to trace unfortunately, I assumed bad/too low Octane gas though.

Since then we've been filling up with 91 premium and have yet to hit the mountain grades again, but it sure seems to run smoother. Is this possible just due to Octane or am I just wishful thinking here?
 
Zstairlessone

Zstairlessone

New member
Remlap said:
Dug up this thread searching about Octane.

Please tell me if I'm just getting a Placebo effect here, but when I was up Camping near Rico CO last month all they had was 86 Octane which I filled with a couple times.

On the way home to AZ through the Flagstaff mountains we got a flashing engine light when hitting near 5K RPM (downshifting uphill), it did this a couple times down here too heading back up the mountains at high RPM's only.

No code was stored to trace unfortunately, I assumed bad/too low Octane gas though.

Since then we've been filling up with 91 premium and have yet to hit the mountain grades again, but it sure seems to run smoother. Is this possible just due to Octane or am I just wishful thinking here?
Click to expand...

Once you come back down from the altitude the lower octane isn't good. You will get knock and the ECU will start cutting back to try to prevent it. Should be ok once you have put enough high octane gas to bring what's in your tank back up with one or two tanks of 91 to run 87 again. I would always run one or two tanks of 89 through and fill with 89 before going down to Grand Junction or over and down to Denver to mix with the 85 in the tank. Learned that after the first trip down when it ran like crap at lower altitudes. Finally just bit the bullet and put mid-grade, which was 87, in all the time cause I couldn't always plan that far ahead. cost more, but meant I could head out for the weekend without a plan.
 
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