Hello guys. i prefer using Mobil on my 2014. i use their highest grade of gas, and found it to be better than using the highest of Hess. Me and my wife calculated the miles and also how much a full tank would last with each brand and found out that paying a little more for Mobil was better as it lasted longer than Hess. Why? i have no clue all i know is that we use the car the same way every day of the week. same route and same miles so we used this as our testing ground. i do belief you should not buy "cheap" gas. i had a 2011 Mazda3 and used the local gas station regular, for about two weeks and my Mazda3 would crank for about a minute before starting. then i used the highest grade of Mobil to flush it all out and never again did it crank longer than it was meant to. best of luck just find what works for you. and keep in mind " you get what you pay for"
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Octane Rating
- Thread starter youzi
- Start date
- :
- 2020 CX-5 GT w/PP
Sorry to repost my question, but I think it got buried by a couple of people name-calling on this thread.
I had asked 2 questions, one about the relationship between recommended octane and high altitude, and one about quality of different brands of gas.
Thank you so much to jjw6455, who posted the link for Top Tier qualified gas stations. (http://www.toptiergas.com/retailers.html)
I found this article about Top Tier, from 2007. Interesting that the few brands the article mentioned as claiming to be better than TT later certified as TT.
http://usatoday30.usatoday.com/money/industries/energy/2007-06-13-bad-gas-usat_N.htm
Does anyone have more to add on that issue, or could anyone touch on the altitude issue? Basically, is it really okay to use 85 octane at 5000 ft altitude?
Thanks. Here is my previous post below, for reference.
I had asked 2 questions, one about the relationship between recommended octane and high altitude, and one about quality of different brands of gas.
Thank you so much to jjw6455, who posted the link for Top Tier qualified gas stations. (http://www.toptiergas.com/retailers.html)
I found this article about Top Tier, from 2007. Interesting that the few brands the article mentioned as claiming to be better than TT later certified as TT.
http://usatoday30.usatoday.com/money/industries/energy/2007-06-13-bad-gas-usat_N.htm
Does anyone have more to add on that issue, or could anyone touch on the altitude issue? Basically, is it really okay to use 85 octane at 5000 ft altitude?
Thanks. Here is my previous post below, for reference.
Way earlier in this thread, MikeM mentioned as a side note, "for example, if the car was fueled with regular that only had an octane of 85 RON (which is actually available in some areas of the US)."
Here in the north front range of Colorado where we're at about 5000 ft altitude, the gas stations sell 85/87/89 rather than 87/89/91. This also seems to be the case in neighboring high-altitude states (Wyoming, Utah); when you go down to lower altitudes (in other states), the higher octane ratings are sold.
Both the Honda dealership and the Mazda dealership here have told me that this is because 85 at high altitude is more or less equivalent to 87 at sea level, and so it's perfectly fine to put 85 octane gasoline in the vehicle here in Colorado. Thoughts on this?
I also found the theme of name brand gas vs. cheaper gas to be interesting; my dad always used to insist on using Union 76 gasoline (in California, they don't have it here), whereas I've always thought gas was gas was gas, and just gone with the cheapest station (our local grocery store usually). Why is/isn't name brand gas better, and has any testing been done which demonstrates this?
Thanks.
Here in the north front range of Colorado where we're at about 5000 ft altitude, the gas stations sell 85/87/89 rather than 87/89/91. This also seems to be the case in neighboring high-altitude states (Wyoming, Utah); when you go down to lower altitudes (in other states), the higher octane ratings are sold.
Both the Honda dealership and the Mazda dealership here have told me that this is because 85 at high altitude is more or less equivalent to 87 at sea level, and so it's perfectly fine to put 85 octane gasoline in the vehicle here in Colorado. Thoughts on this?
I also found the theme of name brand gas vs. cheaper gas to be interesting; my dad always used to insist on using Union 76 gasoline (in California, they don't have it here), whereas I've always thought gas was gas was gas, and just gone with the cheapest station (our local grocery store usually). Why is/isn't name brand gas better, and has any testing been done which demonstrates this?
Thanks.
pjensen641
Member
- :
- 2013 CX-5 AWD Touring Zeal Red
Helen-
It is true that most cars that call for 87 run just fine on 85 at higher altitudes. This is because the lower barometric pressure results in lower peak cylinder pressures at maximum compression. Lower pressures reduce the tendencies for uncontrolled and spontaneous fuel burn known as pre-detonation or Knock. However, In my opinion, I would run mid-grade 87 in the CX. The reason is that the engine has a much higher compression ratio than most cars that are able to burn regular fuel. It is tuned to the bleeding edge of knock and they do many special things to prevent knock. I think there is less margin of safety for the CX than most cars.
The other thing I would say is this. I would want to get it in writing from Mazda USA that they allow 85 at high altitudes before I would use it. Reason is that the manual calls for 87 Minimum. 85 would be grounds for warranty dismissal if you incurred engine damage from knock when all literature warns against it.
And finally, there are some fairly drastic altitude changes in your neck of the woods. If you fill up with 85 up on top, but then take a trip down to lower elevations, what do you do? Stop and drain the tank?
It is true that most cars that call for 87 run just fine on 85 at higher altitudes. This is because the lower barometric pressure results in lower peak cylinder pressures at maximum compression. Lower pressures reduce the tendencies for uncontrolled and spontaneous fuel burn known as pre-detonation or Knock. However, In my opinion, I would run mid-grade 87 in the CX. The reason is that the engine has a much higher compression ratio than most cars that are able to burn regular fuel. It is tuned to the bleeding edge of knock and they do many special things to prevent knock. I think there is less margin of safety for the CX than most cars.
The other thing I would say is this. I would want to get it in writing from Mazda USA that they allow 85 at high altitudes before I would use it. Reason is that the manual calls for 87 Minimum. 85 would be grounds for warranty dismissal if you incurred engine damage from knock when all literature warns against it.
And finally, there are some fairly drastic altitude changes in your neck of the woods. If you fill up with 85 up on top, but then take a trip down to lower elevations, what do you do? Stop and drain the tank?
- :
- 2020 CX-5 GT w/PP
Thanks for your reply, pjensen. You make some very good points. About your last point though, none of the places I regularly drive to are below 4600 ft in altitude... to even get down below 4500 ft, I'd have to be almost to Kansas, and presumably I'd be close to needing a fill-up by the time I drove that far anyway.
Helen, with modern fuel injected cars, you should always keep to the manufacturer's minimum specified octane regardless of the altitude. The reason for this is very simple:
Nowadays, all cars have barometric pressures sensors. They know what your effective altitude is and use that info to adjust engine parameters like ignition advance and fuel mixture to suit. The use of below spec fuel is unanticipated by the ECU.
Do not risk using below spec octane -it's not worth it.
Nowadays, all cars have barometric pressures sensors. They know what your effective altitude is and use that info to adjust engine parameters like ignition advance and fuel mixture to suit. The use of below spec fuel is unanticipated by the ECU.
Do not risk using below spec octane -it's not worth it.
Lets go back over some things. Octane on pumps in the US is AKI (Anti Knock Index) or the average of RON and MON, two different ways to measure octane. All pumps in the US are labeled with the AKI number, although they could have other numbers as well. Apparently Colorado decided on 85 some time ago. It is true, for a normally aspirated (not turbocharged or supercharged) car, the higher the altitude, the lower the octane requirement. So, a car tuned at sea level probably works fine at altitude in Colorado.
However, modern cars are not "tuned", they have multiple computers to continuously adjust the gas and spark to adjust the operation. They listen very, very closely for ping to occur, and can hear it long before you do. They may allow it to progress to a point that you just notice it, but unless it throws a CEL or code, it should be fine. If you run too much ignition advance, or to little fuel, you can damage a modern engine. However, I really doubt that you will do this with a stock CX-5 unless the you are really doing something stupid. I expect the CEL light to come on and shift into limp-home-mode.
Bottom line, I wouldn't worry about using 85 octane gas if that is all that you can find. If you travel to a lower altitude, I would tend to fill up with 87 or whatever is available and keep on trucking. I haven't heard of a case where an engine is damaged by running a computer controlled vehicle with low octane.
Here is an article from Car and Driver from 2001 or so where they tested several different vehicles with regular and premium to see what would happen.
http://www.caranddriver.com/features/regular-or-premium
However, modern cars are not "tuned", they have multiple computers to continuously adjust the gas and spark to adjust the operation. They listen very, very closely for ping to occur, and can hear it long before you do. They may allow it to progress to a point that you just notice it, but unless it throws a CEL or code, it should be fine. If you run too much ignition advance, or to little fuel, you can damage a modern engine. However, I really doubt that you will do this with a stock CX-5 unless the you are really doing something stupid. I expect the CEL light to come on and shift into limp-home-mode.
Bottom line, I wouldn't worry about using 85 octane gas if that is all that you can find. If you travel to a lower altitude, I would tend to fill up with 87 or whatever is available and keep on trucking. I haven't heard of a case where an engine is damaged by running a computer controlled vehicle with low octane.
Here is an article from Car and Driver from 2001 or so where they tested several different vehicles with regular and premium to see what would happen.
http://www.caranddriver.com/features/regular-or-premium
- :
- 2020 CX-5 GT w/PP
Thanks for your replies. I must admit I am not knowledgeable about engines at all, and I am still confused by the differing opinions. So far I have only filled it up once, and I put 87 in it to be safe. To clarify, CXVille, our regular gas here is 85, but we also have 87 available as mid-grade, and 91 as premium. The 87 costs 15 cents more per gallon than the 85.
We have been putting 85 in our '05 Honda Odyssey and '05 Honda CR-V with no effects noticeable to us. But I'm no mechanic.
One section of the Car&Driver article caught my eye: "Hot temperatures and exceptionally low humidity can increase an engine's octane requirements as well. High altitude reduces the demand for octane." We do have high altitude here in Colorado, but we also have low humidity -- as low as 25% in the winter, maybe up to 65% in the summer? We also have 10% ethanol year round at all of the gas stations that I'm aware of.
We have been putting 85 in our '05 Honda Odyssey and '05 Honda CR-V with no effects noticeable to us. But I'm no mechanic.
One section of the Car&Driver article caught my eye: "Hot temperatures and exceptionally low humidity can increase an engine's octane requirements as well. High altitude reduces the demand for octane." We do have high altitude here in Colorado, but we also have low humidity -- as low as 25% in the winter, maybe up to 65% in the summer? We also have 10% ethanol year round at all of the gas stations that I'm aware of.
Bottom line, I wouldn't worry about using 85 octane gas if that is all that you can find.
If 85 octane is all you can find?
I've traveled all over the Rockies and I've never seen a station that didn't offer at least 87 octane.
But if I was running on empty and 85 was all that was available, however unlikely, I would put enough 85 in to get me to a station with gas that met the manufacturers minimum requirements. But it's not worth it to try to save less than 2 bucks when approved fuel is available.
BTW, modern cars are not designed to normally use the knock sensor to avoid detonation. The sensor is there to prevent serious engine damage should something go wrong. Because high altitude is sensed by the barometric pressure sensor and this causes the ECU to advance the timing (and inject less fuel), high altitude is already compensated for automatically. Trying to cheap out by running extra low octane fuel because of the thinner air is stupid. It is double compensating. This can bring the emergency knock sensor into play which will cause engine performance to suffer.
If 85 octane is all you can find?
I've traveled all over the Rockies and I've never seen a station that didn't offer at least 87 octane.
But if I was running on empty and 85 was all that was available, however unlikely, I would put enough 85 in to get me to a station with gas that met the manufacturers minimum requirements. But it's not worth it to try to save less than 2 bucks when approved fuel is available.
BTW, modern cars are not designed to normally use the knock sensor to avoid detonation. The sensor is there to prevent serious engine damage should something go wrong. Because high altitude is sensed by the barometric pressure sensor and this causes the ECU to advance the timing (and inject less fuel), high altitude is already compensated for automatically. Trying to cheap out by running extra low octane fuel because of the thinner air is stupid. It is double compensating. This can bring the emergency knock sensor into play which will cause engine performance to suffer.
I disagree with this assertion. I have tuned my previous Subaru, and had had ignition and fuel "trims" to set the designed operating points. But these trims were set by the O2 sensor for the fuel, and the knock sensor for the timing. It would slowly advance timing till it heard knock, then back off somewhat. It was my understanding that the car continuously did this and adjusted for conditions. It had adjustments for rpm, coolant temp, ambient temp, air intake temp, humidity, rpm, engine load, throttle position, gear, intake pressure, and probably a few other things as well. Some were tables of data, others were modifiers that shifted the entire table. If the trim range was not adequate, for example the starting ignition timing was 40BTDC, and the range of adjustment was +/- 15, and the operating condition required 20BTDC, then it would go into "lime mode" and set the CEL. There were short term and long term trims, which were not adjustable by me, but the computer adjusted them based on inputs.
I could watch the short term trims change during the day as conditions changed. The knock sensor was most definitely making adjustments continuously. As temp went up, a little more timing was removed. Keep in mind that every engine is different. Different tolerances, different operating conditions, different modifications - like a nifty "Cold Air Intake" (CAI) that actually brings in hotter air because of a poor design. The engine adapts just fine. Or, more load, which requires less ignition advance. Lots and lots of variables in play that make using the knock sensor advantageous.
It was my understanding that the engine had trims stored for a variety of conditions that started where the car operated, and then it was fin tuned with the knock sensors and O2 sensors.
While I don't know how the Mazda engines run, I expect they run the same way to maximize performance and fuel economy, something they are very good at.
Thanks for your replies. I must admit I am not knowledgeable about engines at all, and I am still confused by the differing opinions. So far I have only filled it up once, and I put 87 in it to be safe. To clarify, CXVille, our regular gas here is 85, but we also have 87 available as mid-grade, and 91 as premium. The 87 costs 15 cents more per gallon than the 85.
We have been putting 85 in our '05 Honda Odyssey and '05 Honda CR-V with no effects noticeable to us. But I'm no mechanic.
One section of the Car&Driver article caught my eye: "Hot temperatures and exceptionally low humidity can increase an engine's octane requirements as well. High altitude reduces the demand for octane." We do have high altitude here in Colorado, but we also have low humidity -- as low as 25% in the winter, maybe up to 65% in the summer? We also have 10% ethanol year round at all of the gas stations that I'm aware of.
Hot temperatures and low humidity will cause a reduction in ignition timing caused be knock. I believe that the car continuously senses knock and adjusts the timing to be right at the edge. That is how the fuel mileage is maximized. A car makes maximum power when the ignition is advanced as much as possible. It can vary from 5 degrees after Top Dead Center (TDC) to over 40 Before TDC (BTDC). And it is based on a whole slew of conditions - air temp, humidity, load, gas, how hot the engine and engine compartment is, coolant temp, etc.
Everyone of these conditions requires a different set of fuel and ignition timing for maximum efficiency and power. This is why they use a computer with a multitude of sensors - to maximize power which maximizes fuel economy.
If the Mazda dealer recommends it, and everybody else is doing it, I say the 85 is fine. It probably had 85 in it when you bought it. Is there a risk? Yes, very tiny. If you have an engine failure caused by detonation (knock) and they find out you have been using 85 octane, they **MIGHT** chose to not warrant the engine. I've never heard of a modern, unmodified, normally aspirated (no turbocharger or supercharger) engine failing from detonation. The savings at $0.15/gallon and 15,000 miles per year at 25 mpg is about $90 per year.
Your choice.
Yes, since none of us here are on the inside working as Mazda engineers, some speculation is involved regarding ignition, etc.
But specific to topic on hand, I will only use the fuel/octane rating specified by Mazda for the CX-5 (87 octane), not 85 octane.
But specific to topic on hand, I will only use the fuel/octane rating specified by Mazda for the CX-5 (87 octane), not 85 octane.
The savings at $0.15/gallon and 15,000 miles per year at 25 mpg is about $90 per year.
There is only a savings if the 85 octane fuel doesn't cause the ECU to load more conservative maps with reduced ignition advance which require more fuel to travel the same distance. And this assumes the long term efficiency and reliability of the engine isn't negatively impacted. And it ignores the downside of less power and less torque when the ECU needs to load more conservative map tables.
A one MPG hit from reduced ignition advance would completely wipe out that measly $0.15 extra per gallon that it costs to run fuel that meets the manufacturers minimum requirements. And that's not taking into account any possible ill effects that could cost $$ down the road.
Furthermore, if the ECU does constantly advance timing until it senses detonation (as you claim), running 85 octane will guarantee the running of less advance to achieve the same point of maximum combustion pressure. The downside to this is the faster flame front will have less time to transfer heat and the combustion hot spots near the head and valves will be more concentrated. Even though the engine can likely handle that without self-destructing (at least in the case of high-altitude), it is not optimum. At lower altitutudes or at questionable humidifiers, temperatures and loads, all bets are off. Do you really want your engine running near the edge of it's safe design limits?
But, as you correctly point out, the decision is each owner's to make for themselves. They are the ones who will need to shoulder the burden if that 25 cents per day in potential savings (again, assuming no MPG loss) turns into an expensive headache. I could live with a reduction in power because my 2.0L makes more than I need when I use the rpm's but I guess I'm just not that interested in trying to save a couple bucks when I fill up. And at well over 400 miles per tank, those fill-up's are few and far between.
I will only use the fuel/octane rating specified by Mazda for the CX-5 (87 octane), not 85 octane.
I would normally consider that common sense.
But after reading this thread I'm going to venture that your IQ is above average. (lol2)
I would normally consider that common sense.
But after reading this thread I'm going to venture that your IQ is above average. (lol2)
lol, I too will venture to guess we can all find better ways to save a couple bucks.
- :
- 2020 CX-5 GT w/PP
Thanks again for all your input. All of it is appreciated. Am I willing to risk problems with engine and/or warranty for a maximum savings of $100 per year? No. The '05 Honda Odyssey (which I also own) is notorious for having transmission and brake problems caused in part by not using OEM fluids. I don't want to take the chance that the Mazda CX-5's engine is persnickety enough that it will have problems down the road from using 85 octane gasoline.
