85 vs 87 Gas

[MilesTeg]

Hi All,

I was wondering something, in light of the rising gas prices. I live in Colorado, where regular gas is only 85 octane, not 87. Anyway, I've always put plus in my X, since it says to use 87 (plus == 87 in Colorado).

Is there any reason not to use 85? Does it mess up mileage or cause some sort of problem with the engine in other ways? I've been told the engine might knock with only 85, is this true?

Thanks,
MilesTeg

 

[Alec]

You can use less octane with altitude. So effectively you've been using 89.

 

[MrShorty]

I asked this question once (might have even been on this forum). Difference is altitude. As you go up in altitude, octane requirements decrease from the lower ambient pressure. I'm not sure how they decide it, but it seems as I travel the west, above about 3000 feet elevation, regular grade shifts from 87 to 85. At your altitude, you should be fine with 85 octane.

 

[Joey P]

Yeah, I'll agree with that. I've been using 85 all of my driving life so far and have had no adverse side affects. It's all been in the mountains of Colorado too.

 

[Ford_Racing_Guy]

wow thats interesting, i did not know about the altitude thing

 

[MONMIX]

I never knew 85 existed.
Well, that is the price I pay for being a Marylander.

 

[wpurple]

so does that make 85 cheaper than 87? or do they just charge the same and make more profit?

 

[Jason94sport]

I never knew 85 existed.

Same here!

 

[Charlie's_93EB]

Same here!

same here!!

i can buy 115-120 octain i can't remeber which one

 

[Charlie's_93EB]

Same here!

same here!!

i can buy 115-120 octain i can't remeber which one at a gas station 20 miles from here

 

[MilesTeg]

I never knew 85 existed.
Well, that is the price I pay for being a Marylander.

And I never knew that 85 was not used everywhere =)

 

[MilesTeg]

so does that make 85 cheaper than 87? or do they just charge the same and make more profit?

Hmm, while on my trip, it seemed that prices were actually overall cheaper in the places that had 87 as the regular grade, so I can't really tell you for sure. Though, here in CO, the price of regular (85) is about 2/gal and plus (87) is 2.10/gal.

Sadly, I was using (out of habit) the "Plus" even when the regular was 87 until I noticed the octane difference.. whoops!

 

[MilesTeg]

I asked this question once (might have even been on this forum). Difference is altitude. As you go up in altitude, octane requirements decrease from the lower ambient pressure. I'm not sure how they decide it, but it seems as I travel the west, above about 3000 feet elevation, regular grade shifts from 87 to 85. At your altitude, you should be fine with 85 octane.

Yeah, in CO, regular is 85, in New Mexico (NE) the regular was 86, and in TX/OK, the regular was 87. I was pretty sure it had something to do with altitude from that.

 

[Alec]

Keep in mind that if you're filling up at a higher altitude but will be traveling to a lower one (where gas is sold at the higher octane levels), you should fill up to the octane level required at the lower altitude.

 

[karl_burns]

The best 85....

is E-85. I wish our Explorers ran on that. I'd be in hog heaven right now. I know you can purchase the dual fuel inners for about a grand, but I don;t think anyone on this board has done so.....
Actually, two weeks ago some stations in Minnesota ran a special: Gallon of E-85 for 85 cents! How awesome is that?!?!
Karl

 

[cfkane]

Octane requirements drop approximately 1 point per 1000 feet in altitude per API and SAE testing for normally aspirated engines. So if one has an 87 octane requirement at sea level one theoretically could run 82 octane at 5000 feet and be safe. The problem is twofold. At higher altitude people tend to push an engine harder due to the drop in power output and thus any deposits could create problems with lower octane fuel. Second, when one drives to a lower altitude on fuel purchased at high altitude there needs to be enough headroom in the fuel to allow for a safe transition. Thus one generally does not see fuel lower than 85 octane at high altitude.

 

[Makahveli]

ok good to know these things, I'm about to reprogram a dual diablo chip and was wondering why nobody ever mentioned a program for 85 octane. there for a 93 octane chip here is great for 91 octane which is commonly the highest octane you can find at the average gas station here. they are 85, 87, and then 91