85 octane... Wth?

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Saw this all over in Idaho and Utah. You won't open a manual for a car made in the last 15 years that says anything below 87 is OK. So what's the deal? Is it just a cash grab so they can list their 85 the same as everyone else's 87 then charge you more for their 87?
 
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In the areas of high altitude, such as Colorado, Utah, and possibly some other parts of the country, it is generally OK to run slightly lower octane. Most owner's manuals do mention that, too.

Quote:
Q:
I live in Arizona and use 87-octane regular. In Utah, Idaho and Nevada, stations were selling 85-octane as regular gas. This forced me to pay more for midgrade 87-octane. Is this the latest petroleum-industry scam to get more of our money? Will my car run okay on this bogus 85-octane regular?



A:
Octane is the ability of a fuel to resist knock, and high-compression engines tend to knock more. The obverse of that is that lower-compression engines can run on lower-octane gas. Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Cars will run just fine on lower-octane fuel when they're well above sea level--and all of those states are. Hopefully, by the time you get back down to denser air, you've burned off most of the low-octane stuff, and can refill the tank with higher-grade fuel.

http://www.popularmechanics.com/cars/how-to/a5308/4345737/
 
What makes it OK? The fact that the engine can't get as much air so there's less fuel and less matter to compress, making the predet less likely?
 
Originally Posted By: horse123
What makes it OK? The fact that the engine can't get as much air so there's less fuel and less matter to compress, making the predet less likely?

I guess it depends on your engine's compression. See the Q&A I added to my earlier post.

I would guess that in a turbo engine (there are more and more of these out there now), you probably don't want to use the lower octane stuff, regardless of altitude.
 
Yup. Less dense air means much less likely to have spark knock.

The compression ratio of the engine remains the same, but the end effect is the same as having a lower compression engine at lower altitudes.
 
Less air, lowers compression, lower octane can be used.

I always use what's cheapest when in the mtns, or anywhere else for that matter.
 
Originally Posted By: Quattro Pete
Originally Posted By: horse123
What makes it OK? The fact that the engine can't get as much air so there's less fuel and less matter to compress, making the predet less likely?

I guess it depends on your engine's compression. See the Q&A I added to my earlier post.

I would guess that in a turbo engine (there are more and more of these out there now), you probably don't want to use the lower octane stuff, regardless of altitude.


That depends on the amount of boost that the turbo can deliver and what the BOV is at.
 
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At my Roswell location, (3570 altitude) they use 86. No problems with it when I go to Ruidoso (aprox 6500 altitude) or Capitan ((aprox 7400 altitude). This is with my previous Continentals, Maurader and present MKZ. Have not yet been out there with the E350 Cabrio.
 
85 is regular here but I still run 87. Even at 8,000+ feet above sea level, in the summer, going up steep roads, 85 makes cars ping like crazy.

I do run 85 in the winter though. It actually seems to run better when it's cold with 85.
 
Normal stuff in high altitude areas and generally works fine where 87 octane is used and you will remain at higher altitude. Won't use in a turbo vehicle, but in NA its fine.

Ran it for years when I lived in Colorado and still do when I visit.

And it has nothing to do with the E0 vs E10 - the 85 octane in high altitude areas is generally E10.
 
Altitude reduces the octane requirement of an engine. Newer vehicles are better able to adjust for altitude.

State by State Gasoline regulations- https://www.afpm.org/State-Motor-Fuels-Specifications/


Here is a little info from SAE (it is almost 30 years old)-

Octane Number Requirements of Vehicles at High Altitude

Past tests of vehicles show that their octane number requirements decrease with altitude. As a result, gasoline marketers sell lower-octane-number (ON) gasoline in the mountain states and other high-altitude areas. The current ASTM specifications, which allow reduction of gasoline octane of 1.0 to 1.5 ON per thousand feet, are based on CRC test programs run on 1967 to 1972 model vehicles. However, many new vehicles are now equipped with sophisticated electronic engine systems for control of emissions and improvement of performance and fuel economy at all altitudes. Because these new systems could minimize the altitude effect on octane requirement, Amoco Oil tested twelve 1984-1986 model cars and light trucks. We found their ON requirements were reduced on average about 0.2 ON per thousand feet on an (R+M)/2 basis (RMON/1,000 feet).
 
Yeah, I always ran the midgrade when I was traveling recently through the mountainous regions. Didnt know when I was going to end up at a lower elevation and didn't want to be caught with 85 in the tank.
 
Originally Posted By: MNgopher
Normal stuff in high altitude areas and generally works fine where 87 octane is used and you will remain at higher altitude. Won't use in a turbo vehicle, but in NA its fine.



Agreed. Modern turbocharged engines are controlled to achieve a certain manifold absolute pressure before opening the wastegate(s). So if it is running at altitude, the turbo will spin faster to make higher boost pressure, and the engine will make the same power as it does at sea level. Not a good time to put lower octane fuel in.
 
Originally Posted By: Colt45ws
Yeah, I always ran the midgrade when I was traveling recently through the mountainous regions. Didnt know when I was going to end up at a lower elevation and didn't want to be caught with 85 in the tank.

I will be moving in a few weeks to a town at about 5,000 ft elevation. I will continue to use 87 in the Burb because we will need to make periodic runs to a city at about 2,800 ft elevation to make Costco runs every two or three weeks and don't want to have to worry about what's in the tank, particularly because all trips other than those 90 mile hauls will likely be 5 miles or less so a tank may last the entire time between such trips. And I will continue to run premium (whatever that may be) in the GP because of the supercharger.
 
Originally Posted By: shanneba
Altitude reduces the octane requirement of an engine. Newer vehicles are better able to adjust for altitude.

State by State Gasoline regulations- https://www.afpm.org/State-Motor-Fuels-Specifications/


Here is a little info from SAE (it is almost 30 years old)-

Octane Number Requirements of Vehicles at High Altitude

Past tests of vehicles show that their octane number requirements decrease with altitude. As a result, gasoline marketers sell lower-octane-number (ON) gasoline in the mountain states and other high-altitude areas. The current ASTM specifications, which allow reduction of gasoline octane of 1.0 to 1.5 ON per thousand feet, are based on CRC test programs run on 1967 to 1972 model vehicles. However, many new vehicles are now equipped with sophisticated electronic engine systems for control of emissions and improvement of performance and fuel economy at all altitudes. Because these new systems could minimize the altitude effect on octane requirement, Amoco Oil tested twelve 1984-1986 model cars and light trucks. We found their ON requirements were reduced on average about 0.2 ON per thousand feet on an (R+M)/2 basis (RMON/1,000 feet).

I think the 1.0 to 1.5 ON reduction is still the standard as I have seen 85.5 regular (87 - 1.5) in Montana and Wyoming.
 
The guys at Exmark wanted me to run nothing lower than 89 because they want you to get more
additives in the fuel. I use 87 and just use an ethanol treatment which they suggested at each use as well.
That was the choice 89+ or 87 with Star Tron- their suggestions

Originally Posted By: WylieCoyote
I see lawn crews pumping from the 85 pump all the time. A lawn mower is the only thing I'd use 85 in.
 
Originally Posted By: AirgunSavant
The guys at Exmark wanted me to run nothing lower than 89 because they want you to get more
additives in the fuel. I use 87 and just use an ethanol treatment which they suggested at each use as well.
That was the choice 89+ or 87 with Star Tron- their suggestions

Originally Posted By: WylieCoyote
I see lawn crews pumping from the 85 pump all the time. A lawn mower is the only thing I'd use 85 in.


Makes no sense.. generally speaking 89 has no more "additives" than 87.
 
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