Mike and Trish
Mt. Airy, MD
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Joined: 03/02/2008
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Don't waste your money! 85 octane at altitude = 87 at sea level. Remember that octane merely measures resistance to pre-ignition, or "knock," not any measure of power. With thinner air at high altitude, your fuel/air mixture is naturally richer, and not as prone to knocking, thus octane doesn't need to be as high.
Whether at altitude or sea level, using a higher octane than called for in your vehicle is a complete waste of money -- it will not get better mileage, run better, etc., will only drain your wallet faster. on the other hand, using regular in an engine that wants premium won't necessarily make it knock; these days, computer controls on many engines will adjust to avoid knocking, but will cost you power.
Use the grade (don't worry about the octane if at altitude) that your engine manufacturer specifies, and you should be fine. Only upgrade if your engine knocks.
Yes, I know what I'm talking about -- oil company marketing vet and DOE analyst.
Mike and Trish
2008 Mandalay 43A
2008 Jeep Liberty on Blue Ox towbar
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Itchey Feet
Wyoming
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Cannot speak for a Ford, but I have a 8.1 in a 06 GMC, it has had nothing but 85 in it since it was new, been to about every western state and some in Canada. In Feb. we went down to Death Valley and had no Knocks and the milage was the same as when we went to Yellowstone, 8000' +. It is your money and you get to spend it on anything you want to. JMHO
My feet are fine as long as they are traveling.
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rondeb
Pacific Northwest
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We fill half with the 85 and half with the 88. I don't trust the 85 with the v-10. Look for Shell Stations in Montana, Wyoming, that area. They most all still have 87.
* This post was
edited 06/04/10 10:11pm by rondeb *
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pkunk
Questa, NM
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Joined: 12/28/2007
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I run mostly 85 here and have found that the only detriment to mpg is the Da*n E10. I still get a solid 8mpg at highway speeds. It has 10% less BTU's that full gas and so almost 10% less MPG. The wife's car specs 91 octane and we run 87 mid grade with no ill effects.
1999 Coachman Mirada 34 ft.V10-F53 chassis
12ft.LR slide-2 gp31 AGM 12V @220AH
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smkettner
Southern California
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Unless you have a turbocharger or blower to make up for the thin air the 85 is fine.
The effect of altitude is similar to reducing your compression ratio.
2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
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bryantclan
Denver Colorado
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downtheroad wrote:We were used a tank full or two while towing with our Expedition.
I could most certainly feel the difference, especially on grades and long pulls.
It didn't seem to do any damage to the engine.
You will probably really feel it in your big block V10.
If I were to do it again, I'd suck it up and pay for the higher octane.
The "difference" you where feeling has nothing to do with the octane but rather the fact that you where at a minimum 5000 feet MSL (above sea level) at that altitude you loss nearly 25% of your HP.
I live in Denver and make trips to the west coast 2 or 3 times a year and our RV feels like a race car at sea level.
One thing to consider is where you are going with that tank of gas, most of us have a 700+ mile range and you could easily find your way to an altitude that 85 would not be a good plan. Our Jeep gets real unhappy when we first unhook it in San Diego after pulling it from Denver if I forget to put some 87 in it before I leave.
Shaun & Jarese
3 Kids, Nicholas 12, Alex 8, Cassie 5 Years
Denver, Co
Newmar AllStar 3950 (mid-engine diesel)
2007 Honda Odyssey EX-L Toad or Jeep Grand
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TexasH
Katy, TX
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Use 85 in high elevations, but if you are headed back to lower elevations, don't fill up with 85 and drive to the lower places. Use the 87 or get just enough 85 to get you to the lower elevations. Some oil company engineers (in fuels R&D) that I used to know said you're just wasting money on higher octane gas if the stuff you have doesn't make the engine ping under load.
2002 Southwind 37U Ford F53 - V10
2007 Jeep Liberty Toad
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sc3283
St Louis
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most likely your truck is equipped with a knock sensor to constantly adjust timing if a knock is present...use the 85 and don't worry..you have a lot of good info above....(ie..elevation, oxygen level at hi altitude etc)
04 D-Max Crew Dually
96 Monaco Dynasty 36'
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Gale Hawkins
Murray, KY
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I agree you should be fine in that new of an engine.
We use premium in our old 1992 454 with TBI because net cost is the same as for 87 at sea level or just above. The extra mileage gives us a little more range.
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Turbo Diesel Dude
Green Mountain, NC
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For my $$$ any fuel that alchohol is in really sucks!!! Less milage/power etc for the $$$ spent etc, Politicians and their ideas mostly are stupid. There is one station where I live that sells straight gas and I use the plain 87 octane and my DWs Lumina gets about 4 more MPG. Costs about .10 more per gallon, but well worth it for my $$$. The Lumina is a 1996 model 3.1. Not much savings in my mind using MORE fuel. JMHO
charles weidman
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