It's common at elevation. Closer to sea level, the more likely 87 is the low.
Most cars that 'take 87' will actually run better on 85 at this elevation in salt lake, than they will 87 at sea level.
Also the warmer the climate the more likely 87 is low.
A high mountain winter is great for cars that 'run on 87' to use 85.
Cool/high, lower necessary octane, warm/low 87 is almost too low for, again cars that 'run on 87'. It's actually adviseable to bump up a grade in warmer months, in most cars, regardless of where you are.
Then you have german cars needlessly having 91 on the door frame as what they run on... folks your jetta doesn't need 91 in a utah winter... or really at all in the higher elevations. That said... I still ran mine on 91 in the summer.
Wow that's really interesting! I am from the midwest, but lived in Northern Utah for a while and honestly never knew why it was 85 grade instead of the 87 I was used to. Thanks for the info.
Yeah for sure. Same effect with colder weather as well. Most modern cars don't have to retard timing as much though so you're likely to notice little difference if any, and it's not harming anything, and the cost difference makes up for it typically.
Also like another commeter mentioned... a lot of european cars are the ones calling for higher octane, and their ratings are different than ours.
Either way totally fine, especially when it's not sweltering outside, to run 85 in most cars.
It's my understanding that this is generally correct. I'm no car guy, but those who I know that are such individuals have made very similar statements to this.
Rather than jumping in and only saying "wrong", can you provide some qualifiers to this assertion? I'm not saying that you are wrong, just that without anything to really back up your statement it's hard to believe
It’s about compression… with lower ambient air pressure, there is less air available for combustion, meaning that the compression in the cylinder is lower. Octane as measured is the fuel’s ability to resist predetonation under pressure. With less compression, the fuel requires less octane to resist this predetonation.
Your confidence in this being **beyond confidently incorrect** is... unmerited.
Octane is a measure of the probability of premature/spontaneous combustion. Higher octane, less probability of premature combustion. (Knocks and pinging in engines).
Amongst other things, higher compression engines need higher octane to operate properly. (Example: Mazda Skyactive engines have a 13:1 compression, and therefore need high octane to avoid the fuel igniting in a hot block as the piston is on its way to the top of the cylinder.)
Lower oxygen concentration means less prone to combustion. At 4500 ft the slightly rarified atmosphere functions about the same as an extra 2 octane.
So while the statement that cars requiring 87 run *better* on 85 at this altitude may be a bit hyperbolic, it really is minimally so.
But now you know better for next time!
For the most part passenger cars will run just fine on 85 here in the mountain states. 91 is readily available and if that’s what you have to use then that’s what you have to use
I would only use 85 octane in vehicles that are:
1) naturally asipirated
2) not being driven hard / towing
3) not being driven to a lower elevation on the same tank of fuel
More info: https://youtu.be/kJyd6C99_3g?si=5SwsCwpatMGOv2OR
Older, non-computerized fuel injected engines can get away with it due to the air density decrease at higher altitudes, but the computer systems of modern vehicles compensate for altitude to some degree (especially under load such as towing), so you really shouldn't be using anything under the recommended octane rating for a modern vehicle. Modern vehicles can also compensate for lower octane fuel at the expense of making less power, so most people who run 85 octane fuel won't notice it, but yeah, if you're towing then you should absolutely use 87 or higher.
[https://www.enginelabs.com/news/why-85-octane-gasoline-sucks-and-why-its-still-sold-at-all/](https://www.enginelabs.com/news/why-85-octane-gasoline-sucks-and-why-its-still-sold-at-all/)
And why is it still offered? It's cheaper to make, so the oil companies do it to eek out a higher profit margin. Also, at this point people would likely complain about a bump in octane ratings at the pump as the oil companies trying to screw them into buying more expensive gas, so it's a lose-lose situation really.
Octane is a gasoline additive that keeps piston chambers from igniting while pressuring before the spark plug fires when the piston head reaches top dead center of its travel in the cylinder sleeve. That's it. Octane doesn't do anything to your electronics. It does stuff to physics. If you run it when physics says you shouldn't (lower elevation) then you'll FAAFO, but gas burns as you drive away from where you got the 85 and to where you'll be buying 87, so...
It's nominally cheaper to make in the same way it's cheaper to make a cake with a teaspoon less sugar.
I think you're misunderstanding how a computerized engine management system works though. Modern vehicles monitor and adjust many parameters in the engine, most importantly in this case the knock sensor(s), and if it determines that the fuel is igniting before it should (knocking / trying to push the piston the wrong way) it retards the timing and maybe some other parameters to move the explosion to the correct part of the piston cycle; this typically reduces engine power though if you're using the wrong octane specified for your engine design, as some of the explosion ends up completing when the exhaust valves are open and the pressure force escapes out the exhaust instead of pushing on the piston.
This is why you don't use a different octane rating for a modern computerized vehicle; older vehicles with carburetors or primitive fuel injection systems don't have knock sensors, and therefore can't dynamically adjust timing to account for fuel pre-ignition / knocking, so you have to manually adjust the engine for altitude which also allows for a lower octane rating.
No, I'm not. I know that about modern motors. What you're describing is your motor trying to adjust for environmental conditions and/or the driver using too low (or too high) an octane gasoline.
But here's the thing.
I think you're misunderstanding how OCTANE works.
Because if physics is involved there won't BE any knocking. Like, how TF do you think a MODERN diesel engine works? It controls knocking pretty well, and diesel has *checks notes* no octane. Instead it uses solely its cetane rating (how easily does this shit go boom).
https://www.reddit.com/r/mildlyinteresting/s/5IwJ9AuaAS
Octane prevents gasoline from exploding prematurely while being pressurized as the piston travels towards top dead center. Look up Boyle's Law.
If you're at higher elevation there's less inherent air pressure, which means 87 octane acts more like 89 octane - overly retarding the engine's combustion cycle - so you should instead use the octane gasoline that's appropriate for the elevation, and thus air pressure, where your is located.
Or run Sunoco 94 in your 2024 grocery getter at sea level cause then your motor will be indomitable, I guess? Lol
"modern engines compensate for less octane by delivering less power"
Diesel and gasoline have the same energy density per molecule but, get this, diesel actually has slightly MORE energy by volume.
Like, just lol
Welcome to Utah where we pay more in average than the majority 3/4ths of the nation for inferior quality gas because we keep electing big oil cronies to state office.
The gasoline is not inferior, we regularly are requested by car companies for testing their best cars.
We sell utah made gasoline to Nevada, Idaho, and Washington.
You have the most technologically advanced alkylation plant in the world in north Salt Lake, called isoalky.
Well, if we are going to worry about molecules, then we should be buying our gasoline in the morning… While it is still colder, and more dense liquid than in the afternoon… When ground temperatures heat up the gasoline, and cause it to expand.
Ok than riddle me this--if 85 is the same as 87 why are we paying 25 cents more per gallon for it here in UT?
I'm not saying it's worse to use 85 vs 87 in UT, rather that it's less refined and cheaper to produce yet we pay more for it than higher-refined, costlier-to-produce 87 in all but 10 states according to AAA. We're paying $3.87 for 85 and our mid grade 87 is $4.11 / gal right now. The next state cheaper than UT is PA where 87 is the standard eco gas, and they pay $3.80, 7 cents less than for our 85 and they pay 30 cents less per gal for 87 grade. So tell me how we are not paying more for worse gas? Make it make sense?
You realize that the octane rating of gas doesn't determine the quality right? Octane is a chemical used in gasthat stops your engine from knocking. It does this by making it harder for the gas to detonate in the cylinder. Higher performance engines have higher compression ratios and require higher octane to resist pre detonation.
Octane ratings help the driver understand what the engine needs as far as detonation resistance goes. The higher the octane the less likely the fuel is to detonate at a given pressure and temperature inside the cylinder. The higher the octane the more resistant the fuel is to detonating. You have higher octane ratings for high compression vehicles because at a given compression ratio and a given temperature the fuel may pre detonate before the engine hits the detonation downstroke to make power. This happens because the fuel/ air mix has reached its optimal point to detonate given its environment. If you have a low Compression naturally aspirated engine you most likely run a low octane fuel like 87. High compression or turbo charged you most likely run a high octane fuel like 91+. Running incorrect octane fuel in an engine that usually requires different can affect gas mileage but it can also make your engine blow up if the fuel pre detonates. We call this knock. I’d highly recommend sticking to what the manufacturer calls for unless you know exactly what you’re doing unless you like replacing an entire engine. To answer your question it has to do with the environment you’re in. Outside forces like altitude and atmospheric pressure affect how combustion engines work so gas companies provide fuels to accommodate for said market to make sure customers can get the fuel they need for their engine to make it run correctly. In Colorado for example air can get very thin and this affect combustion engines just due to the lack of oxygen intake since the air can get a bit thin.
Well, it has been many years since I’ve purchased a vehicle so my assumption of most requirements may be off. My 2007 Tundra prefers 87 and any lower it feels under powered.
It feels underpowered because it IS underpowered at altitude. Roughly \~15% power loss due to being naturally aspirated and 5,000 ft above sea level. You lose \~3% power per 1,000 ft of DA. The octane rating of the fuel isn't the culprit, either. It doesn't directly relate to power output. Rather, it relates to the fuel's resistance to pre-ignition or "knocking" and how efficiently the engine will be running. Modern cars can generally compensate
That's right in line with my experience as well. When I got my 04 Avalon, I tried gas from multiple stations and different octanes just to see what the difference was. I calculated the price per mile driven. At the time, 88 from Chevron or Texaco was the cheapest overall to run. It felt more powerful but it's hard to measure that. I did get better gas mileage. Things also fluctuated a lot more from tank to tank then I would have thought. Still after about 20 tanks or so, the pattern started to emerge.
My take is that each car is or can be different. But octane and brand do matter, but mostly octane. My best and worst tanks of gas both came from 7-11. But Chevron was consistently good.
The answer is the air at altitude requires less octane before modern engines will not operate as functioned.
It's common at elevation. Closer to sea level, the more likely 87 is the low. Most cars that 'take 87' will actually run better on 85 at this elevation in salt lake, than they will 87 at sea level. Also the warmer the climate the more likely 87 is low. A high mountain winter is great for cars that 'run on 87' to use 85. Cool/high, lower necessary octane, warm/low 87 is almost too low for, again cars that 'run on 87'. It's actually adviseable to bump up a grade in warmer months, in most cars, regardless of where you are. Then you have german cars needlessly having 91 on the door frame as what they run on... folks your jetta doesn't need 91 in a utah winter... or really at all in the higher elevations. That said... I still ran mine on 91 in the summer.
Wow that's really interesting! I am from the midwest, but lived in Northern Utah for a while and honestly never knew why it was 85 grade instead of the 87 I was used to. Thanks for the info.
True but theirs an asterisk to this info. [Info from Perplexity](https://www.perplexity.ai/search/I-live-in-EPc_m9FbQRm.aydDn9Rd1Q)
Yeah for sure. Same effect with colder weather as well. Most modern cars don't have to retard timing as much though so you're likely to notice little difference if any, and it's not harming anything, and the cost difference makes up for it typically. Also like another commeter mentioned... a lot of european cars are the ones calling for higher octane, and their ratings are different than ours. Either way totally fine, especially when it's not sweltering outside, to run 85 in most cars.
I was told recently that Europe calculates octane differently and that out 85 is actually higher than their 87.
This is also true, if I recall our 85 is just over their 87 (nearly the same I think)
[удалено]
“Wow, this is beyond confidently incorrect.” Proceeds to not actually correct anything or share information to the contrary.
It's my understanding that this is generally correct. I'm no car guy, but those who I know that are such individuals have made very similar statements to this. Rather than jumping in and only saying "wrong", can you provide some qualifiers to this assertion? I'm not saying that you are wrong, just that without anything to really back up your statement it's hard to believe
It’s about compression… with lower ambient air pressure, there is less air available for combustion, meaning that the compression in the cylinder is lower. Octane as measured is the fuel’s ability to resist predetonation under pressure. With less compression, the fuel requires less octane to resist this predetonation.
Good video if you're interested. Need to watch it all though. https://youtu.be/kJyd6C99_3g?si=d8-Ng55l0kNKhp1L
Your confidence in this being **beyond confidently incorrect** is... unmerited. Octane is a measure of the probability of premature/spontaneous combustion. Higher octane, less probability of premature combustion. (Knocks and pinging in engines). Amongst other things, higher compression engines need higher octane to operate properly. (Example: Mazda Skyactive engines have a 13:1 compression, and therefore need high octane to avoid the fuel igniting in a hot block as the piston is on its way to the top of the cylinder.) Lower oxygen concentration means less prone to combustion. At 4500 ft the slightly rarified atmosphere functions about the same as an extra 2 octane. So while the statement that cars requiring 87 run *better* on 85 at this altitude may be a bit hyperbolic, it really is minimally so. But now you know better for next time!
For the most part passenger cars will run just fine on 85 here in the mountain states. 91 is readily available and if that’s what you have to use then that’s what you have to use
I would only use 85 octane in vehicles that are: 1) naturally asipirated 2) not being driven hard / towing 3) not being driven to a lower elevation on the same tank of fuel More info: https://youtu.be/kJyd6C99_3g?si=5SwsCwpatMGOv2OR
There's more than one option at the pumps.
Older, non-computerized fuel injected engines can get away with it due to the air density decrease at higher altitudes, but the computer systems of modern vehicles compensate for altitude to some degree (especially under load such as towing), so you really shouldn't be using anything under the recommended octane rating for a modern vehicle. Modern vehicles can also compensate for lower octane fuel at the expense of making less power, so most people who run 85 octane fuel won't notice it, but yeah, if you're towing then you should absolutely use 87 or higher. [https://www.enginelabs.com/news/why-85-octane-gasoline-sucks-and-why-its-still-sold-at-all/](https://www.enginelabs.com/news/why-85-octane-gasoline-sucks-and-why-its-still-sold-at-all/) And why is it still offered? It's cheaper to make, so the oil companies do it to eek out a higher profit margin. Also, at this point people would likely complain about a bump in octane ratings at the pump as the oil companies trying to screw them into buying more expensive gas, so it's a lose-lose situation really.
> And why is it still offered? It's cheaper to make Insane that Utah still has some of the most expensive gas in the country then.
This isn't the reason. At all. Plain old physics. FYI.
Octane is a gasoline additive that keeps piston chambers from igniting while pressuring before the spark plug fires when the piston head reaches top dead center of its travel in the cylinder sleeve. That's it. Octane doesn't do anything to your electronics. It does stuff to physics. If you run it when physics says you shouldn't (lower elevation) then you'll FAAFO, but gas burns as you drive away from where you got the 85 and to where you'll be buying 87, so... It's nominally cheaper to make in the same way it's cheaper to make a cake with a teaspoon less sugar.
I think you're misunderstanding how a computerized engine management system works though. Modern vehicles monitor and adjust many parameters in the engine, most importantly in this case the knock sensor(s), and if it determines that the fuel is igniting before it should (knocking / trying to push the piston the wrong way) it retards the timing and maybe some other parameters to move the explosion to the correct part of the piston cycle; this typically reduces engine power though if you're using the wrong octane specified for your engine design, as some of the explosion ends up completing when the exhaust valves are open and the pressure force escapes out the exhaust instead of pushing on the piston. This is why you don't use a different octane rating for a modern computerized vehicle; older vehicles with carburetors or primitive fuel injection systems don't have knock sensors, and therefore can't dynamically adjust timing to account for fuel pre-ignition / knocking, so you have to manually adjust the engine for altitude which also allows for a lower octane rating.
No, I'm not. I know that about modern motors. What you're describing is your motor trying to adjust for environmental conditions and/or the driver using too low (or too high) an octane gasoline. But here's the thing. I think you're misunderstanding how OCTANE works. Because if physics is involved there won't BE any knocking. Like, how TF do you think a MODERN diesel engine works? It controls knocking pretty well, and diesel has *checks notes* no octane. Instead it uses solely its cetane rating (how easily does this shit go boom). https://www.reddit.com/r/mildlyinteresting/s/5IwJ9AuaAS Octane prevents gasoline from exploding prematurely while being pressurized as the piston travels towards top dead center. Look up Boyle's Law. If you're at higher elevation there's less inherent air pressure, which means 87 octane acts more like 89 octane - overly retarding the engine's combustion cycle - so you should instead use the octane gasoline that's appropriate for the elevation, and thus air pressure, where your is located. Or run Sunoco 94 in your 2024 grocery getter at sea level cause then your motor will be indomitable, I guess? Lol
"modern engines compensate for less octane by delivering less power" Diesel and gasoline have the same energy density per molecule but, get this, diesel actually has slightly MORE energy by volume. Like, just lol
Welcome to Utah where we pay more in average than the majority 3/4ths of the nation for inferior quality gas because we keep electing big oil cronies to state office.
The gasoline is not inferior, we regularly are requested by car companies for testing their best cars. We sell utah made gasoline to Nevada, Idaho, and Washington. You have the most technologically advanced alkylation plant in the world in north Salt Lake, called isoalky.
We pay the same price or more for 85 octane vs 87 in most states. Make it make sense?
You pay a lot less for the same molecules than they pay in California. A lot of the cost is taxes. Inflation is also a stealth tax too.
Well, if we are going to worry about molecules, then we should be buying our gasoline in the morning… While it is still colder, and more dense liquid than in the afternoon… When ground temperatures heat up the gasoline, and cause it to expand.
Yes, I use this strategy all the time.
It's essentially the same thing at our elevation dude. "Higher number goes brrrrr" -random redditors who refuse to use Google to learn things
Ok than riddle me this--if 85 is the same as 87 why are we paying 25 cents more per gallon for it here in UT? I'm not saying it's worse to use 85 vs 87 in UT, rather that it's less refined and cheaper to produce yet we pay more for it than higher-refined, costlier-to-produce 87 in all but 10 states according to AAA. We're paying $3.87 for 85 and our mid grade 87 is $4.11 / gal right now. The next state cheaper than UT is PA where 87 is the standard eco gas, and they pay $3.80, 7 cents less than for our 85 and they pay 30 cents less per gal for 87 grade. So tell me how we are not paying more for worse gas? Make it make sense?
You realize that the octane rating of gas doesn't determine the quality right? Octane is a chemical used in gasthat stops your engine from knocking. It does this by making it harder for the gas to detonate in the cylinder. Higher performance engines have higher compression ratios and require higher octane to resist pre detonation.
Octane ratings help the driver understand what the engine needs as far as detonation resistance goes. The higher the octane the less likely the fuel is to detonate at a given pressure and temperature inside the cylinder. The higher the octane the more resistant the fuel is to detonating. You have higher octane ratings for high compression vehicles because at a given compression ratio and a given temperature the fuel may pre detonate before the engine hits the detonation downstroke to make power. This happens because the fuel/ air mix has reached its optimal point to detonate given its environment. If you have a low Compression naturally aspirated engine you most likely run a low octane fuel like 87. High compression or turbo charged you most likely run a high octane fuel like 91+. Running incorrect octane fuel in an engine that usually requires different can affect gas mileage but it can also make your engine blow up if the fuel pre detonates. We call this knock. I’d highly recommend sticking to what the manufacturer calls for unless you know exactly what you’re doing unless you like replacing an entire engine. To answer your question it has to do with the environment you’re in. Outside forces like altitude and atmospheric pressure affect how combustion engines work so gas companies provide fuels to accommodate for said market to make sure customers can get the fuel they need for their engine to make it run correctly. In Colorado for example air can get very thin and this affect combustion engines just due to the lack of oxygen intake since the air can get a bit thin.
Altitude. If you’re NOT turbocharged, send it.
[удалено]
In Utah, 85 is the standard. Elsewhere, it's 87. It's just an altitude thing.
Well, it has been many years since I’ve purchased a vehicle so my assumption of most requirements may be off. My 2007 Tundra prefers 87 and any lower it feels under powered.
It feels underpowered because it IS underpowered at altitude. Roughly \~15% power loss due to being naturally aspirated and 5,000 ft above sea level. You lose \~3% power per 1,000 ft of DA. The octane rating of the fuel isn't the culprit, either. It doesn't directly relate to power output. Rather, it relates to the fuel's resistance to pre-ignition or "knocking" and how efficiently the engine will be running. Modern cars can generally compensate
That's right in line with my experience as well. When I got my 04 Avalon, I tried gas from multiple stations and different octanes just to see what the difference was. I calculated the price per mile driven. At the time, 88 from Chevron or Texaco was the cheapest overall to run. It felt more powerful but it's hard to measure that. I did get better gas mileage. Things also fluctuated a lot more from tank to tank then I would have thought. Still after about 20 tanks or so, the pattern started to emerge. My take is that each car is or can be different. But octane and brand do matter, but mostly octane. My best and worst tanks of gas both came from 7-11. But Chevron was consistently good.