Fuel discussions/questions - Octane Regular or Premium (merged threads)
#181
Lexus Champion
After reading a long thread about this six months (or more) ago I started running regular I'd say 75% of the time. 90% of the time I run Chevron in it, occasionally Valero. There is zero difference in gas mileage and I don't feel any difference in performance. I would happily pay for premium fuel for better performance, bit its just not there. And when I read as much as I could find on the Toyota vs Lexus debate, I felt sure we had been duped.
FWIT, I've been a major gearhead for nearly 50 years. I've read a tremendous amount, owned MANY high performance boats, cars, and motorcycles and have some amateur racing experience. I don't claim to be an expert, but I trust what I have learned. If I lived in an area with a lot of hills that puts a greater load on an engine, or if the vehicle was driven hard a lot (it's my wifes) I would probably err towards the need for a higher octane. But neither of those conditions exist for me.
FWIT, I've been a major gearhead for nearly 50 years. I've read a tremendous amount, owned MANY high performance boats, cars, and motorcycles and have some amateur racing experience. I don't claim to be an expert, but I trust what I have learned. If I lived in an area with a lot of hills that puts a greater load on an engine, or if the vehicle was driven hard a lot (it's my wifes) I would probably err towards the need for a higher octane. But neither of those conditions exist for me.
Engines used to ping like crazy in the mountains. I live in Calgary(foothills of Rockies) Pulling 30 feet fiver with an old Ford F250HD Camper special. I had replaced
timing gear to retard timing, put in a different spring set in the distributor to change timing advance curve, change jet orifice in the 4 bbl carb. stuff like that.
Lot of people thinks now engine is under computer control, so nothing to worry. Well computer's ability has a limit too. (BTW, I am retired EE who spend ~45 years
on digital logic .. microprocessor..computer small and super size) Computer is run by program(software, firmware) which is coded by human. No program is perfect.
They are improving all the time but never reached perfect stage yet. The blind idea of computer will take care of all is very wrong.
#182
Lexus LX570 get more power and has less city miles per gallon than the Land Cruiser. I am not buying the MPG argument. If that was the case, then the reason to put premium fuel in is just. Furthermore, Land Cruiser should get better mileage than the EPA estimates with premium.
I'm not understanding the argument you are making. I'm seeing an identical mpg rating for both vehicles you are listing. Both 2017 models get 13 city/ 18 highway.
#183
Lead Lap
From Opplock
I saw this post on fuel octane on LifeHacker. I work at Ford Motor Company as an Advanced Engine Development Engineer and I’d like to clear some things up, since there is some inaccurate advice on that post,
My views/comments are my own and do not necessarily represent those of my employer (We have these monthly online training sessions, and one of them told me to put this if I identify who I am, so hopefully I don’t get in trouble...)
First Some Background on how Octane is determined:
Octane on the fuel pump is known as Anti Knock Index or AKI, and is the average of a fuels Research Octane Number and Motor Octane Number [(R+M)/2]. The MON and RON are determined by using a special engine with variable compression ratio, and comparing the knocking qualities of a given fuel to that of reference fuels, isooctane and n-heptane. MON and RON have different engine operating conditions, like engine speed, intake temperature, etc. The slope created by these two numbers are important to us engineers in understanding a fuel’s knocking quality in various engine conditions (like boosted, vs non boosted). To the average Joe, the average of these two numbers (what you see on the pump) is what matters.
Next, some background on what knock actually is, and what Octane does to prevent it:
In a spark ignited engine, combustion does not occur instantly at all points in the combustion chamber. Combustion starts at the spark plug and propagates outward roughly spherically. Flame speed is determined by many factors, such as tumble, swirl, piston design, etc. The biggest impact on flame speed is engine speed, so as the engine spins faster, combustion occurs faster. (This is very convenient in terms of designing ignition advance and valve timing)
So, what is knock? Well, as the flame front is propagating across the combustion chamber, the unburnt portion, or end gas, experiences and increase in pressure and temperature. If the increase is high enough, the end gas will spontaneously combust. This spontaneous combustion is very fast and rather violent, so it causes the engine structure to resonate. The resonance is what we hear as knock.
What does Octane do? An increase in octane rating of a fuel represents an increase in the fuel’s auto ignition temperature and pressure. It does not change combustion speed or anything like that. So, if the fuel has a higher auto-ignition pressure and temperature, it takes higher pressure and temperature for knock to occur. The actual mechanics of how this works is complicated chemistry, and this post is long enough already...
Now some background on knock sensors.
A knock sensor is a piezoelectric device. When the piezo crystal inside experiences a force, it generates a voltage. That voltage is then measured by the PCM. The important part of this signal is the frequency of the signal. All engine components create vibration, so the PCM must analyze the signal, looking for specific frequencies associated with engine knock. The PCM performs an FFT (Fast Fourier Transform), or some other proprietary algorithm, to translate the signal from time domain to frequency domain. The results of this FFT are then analyzed to determine if the engine is knocking. If it is determined the engine is knocking, timing is reduced to prevent knocking. This is computationally intensive, so it is difficult to do for transients, like tip-ins, tip-outs, engine shifts, etc. Also, if an engine component creates frequencies near the knocking frequency, it can be difficult to distinguish. So, knock detection is mathematically difficult and computationally intensive, so it can be difficult to do in all circumstances.
So, what happens if you put a higher octane than your car requires?
In short, nothing. Absolutely nothing (except waste money). If the engine calls for 87 octane, then the timing is set for 87 octane. If you put in higher octane, say 93, there is no cause for knock concerns, since it is designed for 87 octane.
What about special additives in premium fuels?
Premium fuel does not have any additional detergents, or anything like that. All fuels must meet strict regulations on detergents, octane levels, sulfur contents, etc. etc. This means, other than octane rating, all fuels are created equal, within a certain standard. This standard is actually very important to engine design, so that we engineers know, within a tolerance, what fuel you will always have in your engine. Now, I say within a tolerance, because fuel formulation can change. One particular example is in colder temperatures. In colder temperatures, the evaporation temperature (Volatility) of the fuel can be lowered, allowing for the use of less expensive additives to meet the octane requirements. This is why you may notice a change in fuel economy when comparing summer to winter.
What happens if you put a lower octane than your car requires?
In short, MAYBE nothing. This one is kind of a big risk. The stack exchange article says that a modern knock sensor will correct for lower octane fuel. This is true, but only in steady state conditions; like cruising down the road, or steady uphill, etc. Transient conditions are where the problems lie. Since it does take time to analyze the knock sensor signal, fast changes in engine load or speed, are difficult to prevent knock. Every automaker is going to be different in this regard, since the ability to analyze this knock quickly depends on the skill of the programmers and calibrators and even the speed of the PCM processor. So, if you put in a lower octane fuel, and then go drive your car hard, press the accelerator quickly, it is possible to experience heavy knock, and possible engine damage. I will say, it is unlikely to actually happen in cars produced in the last few years, but you are certainly exposing your engine to the possibility. ALWAYS, ALWAYS, ALWAYS use the fuel recommended in the owners manual of your car, or any signs on the fuel door or cap. When engineers say to use a certain fuel, we have good reasons for doing so.
TLR
Always follow what your manual recommends. If your engine calls for 93 octane, USE 93 octane. Don’t risk engine damage.
My views/comments are my own and do not necessarily represent those of my employer (We have these monthly online training sessions, and one of them told me to put this if I identify who I am, so hopefully I don’t get in trouble...)
First Some Background on how Octane is determined:
Octane on the fuel pump is known as Anti Knock Index or AKI, and is the average of a fuels Research Octane Number and Motor Octane Number [(R+M)/2]. The MON and RON are determined by using a special engine with variable compression ratio, and comparing the knocking qualities of a given fuel to that of reference fuels, isooctane and n-heptane. MON and RON have different engine operating conditions, like engine speed, intake temperature, etc. The slope created by these two numbers are important to us engineers in understanding a fuel’s knocking quality in various engine conditions (like boosted, vs non boosted). To the average Joe, the average of these two numbers (what you see on the pump) is what matters.
Next, some background on what knock actually is, and what Octane does to prevent it:
In a spark ignited engine, combustion does not occur instantly at all points in the combustion chamber. Combustion starts at the spark plug and propagates outward roughly spherically. Flame speed is determined by many factors, such as tumble, swirl, piston design, etc. The biggest impact on flame speed is engine speed, so as the engine spins faster, combustion occurs faster. (This is very convenient in terms of designing ignition advance and valve timing)
So, what is knock? Well, as the flame front is propagating across the combustion chamber, the unburnt portion, or end gas, experiences and increase in pressure and temperature. If the increase is high enough, the end gas will spontaneously combust. This spontaneous combustion is very fast and rather violent, so it causes the engine structure to resonate. The resonance is what we hear as knock.
What does Octane do? An increase in octane rating of a fuel represents an increase in the fuel’s auto ignition temperature and pressure. It does not change combustion speed or anything like that. So, if the fuel has a higher auto-ignition pressure and temperature, it takes higher pressure and temperature for knock to occur. The actual mechanics of how this works is complicated chemistry, and this post is long enough already...
Now some background on knock sensors.
A knock sensor is a piezoelectric device. When the piezo crystal inside experiences a force, it generates a voltage. That voltage is then measured by the PCM. The important part of this signal is the frequency of the signal. All engine components create vibration, so the PCM must analyze the signal, looking for specific frequencies associated with engine knock. The PCM performs an FFT (Fast Fourier Transform), or some other proprietary algorithm, to translate the signal from time domain to frequency domain. The results of this FFT are then analyzed to determine if the engine is knocking. If it is determined the engine is knocking, timing is reduced to prevent knocking. This is computationally intensive, so it is difficult to do for transients, like tip-ins, tip-outs, engine shifts, etc. Also, if an engine component creates frequencies near the knocking frequency, it can be difficult to distinguish. So, knock detection is mathematically difficult and computationally intensive, so it can be difficult to do in all circumstances.
So, what happens if you put a higher octane than your car requires?
In short, nothing. Absolutely nothing (except waste money). If the engine calls for 87 octane, then the timing is set for 87 octane. If you put in higher octane, say 93, there is no cause for knock concerns, since it is designed for 87 octane.
What about special additives in premium fuels?
Premium fuel does not have any additional detergents, or anything like that. All fuels must meet strict regulations on detergents, octane levels, sulfur contents, etc. etc. This means, other than octane rating, all fuels are created equal, within a certain standard. This standard is actually very important to engine design, so that we engineers know, within a tolerance, what fuel you will always have in your engine. Now, I say within a tolerance, because fuel formulation can change. One particular example is in colder temperatures. In colder temperatures, the evaporation temperature (Volatility) of the fuel can be lowered, allowing for the use of less expensive additives to meet the octane requirements. This is why you may notice a change in fuel economy when comparing summer to winter.
What happens if you put a lower octane than your car requires?
In short, MAYBE nothing. This one is kind of a big risk. The stack exchange article says that a modern knock sensor will correct for lower octane fuel. This is true, but only in steady state conditions; like cruising down the road, or steady uphill, etc. Transient conditions are where the problems lie. Since it does take time to analyze the knock sensor signal, fast changes in engine load or speed, are difficult to prevent knock. Every automaker is going to be different in this regard, since the ability to analyze this knock quickly depends on the skill of the programmers and calibrators and even the speed of the PCM processor. So, if you put in a lower octane fuel, and then go drive your car hard, press the accelerator quickly, it is possible to experience heavy knock, and possible engine damage. I will say, it is unlikely to actually happen in cars produced in the last few years, but you are certainly exposing your engine to the possibility. ALWAYS, ALWAYS, ALWAYS use the fuel recommended in the owners manual of your car, or any signs on the fuel door or cap. When engineers say to use a certain fuel, we have good reasons for doing so.
TLR
Always follow what your manual recommends. If your engine calls for 93 octane, USE 93 octane. Don’t risk engine damage.
The following users liked this post:
mcomer (09-01-17)
#184
When I was driving Acura MDX(few of them), owner's manual always had warning saying lower grade fuel may damage the engine. Your statement is very bold.
Are you an automotive engineer? If your engine developed a problem and needs major work under warranty, The dealer service manager says, 'you've been running lower Octane fuel with your car which caused this problems. Warranty is void' Do you have an authority to counter that?
You can hire a lawyer but Lexus can have more lawyers than you can hire.
Are you an automotive engineer? If your engine developed a problem and needs major work under warranty, The dealer service manager says, 'you've been running lower Octane fuel with your car which caused this problems. Warranty is void' Do you have an authority to counter that?
You can hire a lawyer but Lexus can have more lawyers than you can hire.
If you read correctly (from the previous posts) then you would see that I was talking about 2011 vs. 2012 RX350. Same engines, same transmissions, same cars but the 2011 required Premium (91 or higher) while 2012 required Regular (87 or higher). The ONLY reason I can think of is: In 2011 timeframe gas price was increasing like crazy, approaching $4 - $5 per gallon or more in certain places. Lexus knows that buyers would often turn away when they see "Premium Required" sticker; therefore, they slapped the RX350 and ES350 with "Regular Unleaded" stickers and reduced 5 hp.
I am an engineer but not automotive engineer.
The following users liked this post:
Craigyyy (09-14-17)
#185
Lexus Fanatic
My bad. Up until the recent LX transmission update, the LX570 on premium was rated at 12/18 while the Land Cruiser on regular was at 13/18
#186
Lexus Fanatic
For the record. The 2011 RX manual states that 87 octane is OK to use, but decreased performance and possible engine damage could occur.
#187
After reading a long thread about this six months (or more) ago I started running regular I'd say 75% of the time. 90% of the time I run Chevron in it, occasionally Valero. There is zero difference in gas mileage and I don't feel any difference in performance. I would happily pay for premium fuel for better performance, bit its just not there. And when I read as much as I could find on the Toyota vs Lexus debate, I felt sure we had been duped.
FWIT, I've been a major gearhead for nearly 50 years. I've read a tremendous amount, owned MANY high performance boats, cars, and motorcycles and have some amateur racing experience. I don't claim to be an expert, but I trust what I have learned. If I lived in an area with a lot of hills that puts a greater load on an engine, or if the vehicle was driven hard a lot (it's my wifes) I would probably err towards the need for a higher octane. But neither of those conditions exist for me.
FWIT, I've been a major gearhead for nearly 50 years. I've read a tremendous amount, owned MANY high performance boats, cars, and motorcycles and have some amateur racing experience. I don't claim to be an expert, but I trust what I have learned. If I lived in an area with a lot of hills that puts a greater load on an engine, or if the vehicle was driven hard a lot (it's my wifes) I would probably err towards the need for a higher octane. But neither of those conditions exist for me.
Last edited by 1111GS; 09-03-17 at 09:06 AM.
#188
as to your link to the response from Lexus, that was a very softly worded response that meant nothing to me. It's exactly what I would expect to support their "requirement".
As as far as why they would recommend it, that could be a variety of reasons. But as long as I believe the Lexus and Toyota engine are identcial other than minor differences in the exhaust system, which I do believe they are, then I really don't care what Lexus reason is.
#189
Thanks for the post. I'm not after the saving and always follow manual recommendations. It's a relief to see your post. I did some reading and it seems the potential problem is engine knocking but some vehicles can compensate to prevent that. Maybe our vehicle is one of those? Did you do this on the GS as well?
Yes, some engines are designed to "hear" knocking, which is pre detonation, and automatically adjust the timing to prevent it. Most vehicles that are designed solely for regular gas are simply designed not to pre detonate under any conditions and don't need knock sensors.
#190
I agree with you. At lower elevation or sea level. Engines may not complain on lower Octane fuel. B4 the days of ECU, fuel injection and electronic ignition, etc.
Engines used to ping like crazy in the mountains. I live in Calgary(foothills of Rockies) Pulling 30 feet fiver with an old Ford F250HD Camper special. I had replaced
timing gear to retard timing, put in a different spring set in the distributor to change timing advance curve, change jet orifice in the 4 bbl carb. stuff like that.
Lot of people thinks now engine is under computer control, so nothing to worry. Well computer's ability has a limit too. (BTW, I am retired EE who spend ~45 years
on digital logic .. microprocessor..computer small and super size) Computer is run by program(software, firmware) which is coded by human. No program is perfect.
They are improving all the time but never reached perfect stage yet. The blind idea of computer will take care of all is very wrong.
Engines used to ping like crazy in the mountains. I live in Calgary(foothills of Rockies) Pulling 30 feet fiver with an old Ford F250HD Camper special. I had replaced
timing gear to retard timing, put in a different spring set in the distributor to change timing advance curve, change jet orifice in the 4 bbl carb. stuff like that.
Lot of people thinks now engine is under computer control, so nothing to worry. Well computer's ability has a limit too. (BTW, I am retired EE who spend ~45 years
on digital logic .. microprocessor..computer small and super size) Computer is run by program(software, firmware) which is coded by human. No program is perfect.
They are improving all the time but never reached perfect stage yet. The blind idea of computer will take care of all is very wrong.
#191
Thanks for the nice post. I'm not an engineer and have not even played one on TV. But I have read a lot and actually am in the electrical industry. I try not to act like I know things I don't know which is why I say I trust what I have learned. But you'll notice I'm not suggesting anyone do what I'm doing and I'm not criticizing anyone for not agreeing with me or continuing to use premium. I get where they are coming from. I'm simply stating my reasons for doing what I am doing.
#192
Lexus Fanatic
Premium gasoline does not give better performance unless the engine is designed to need it. In fact, quite the contrary. Premium fuel burns slower than lower octane fuel. That means that if the engine does not need premium lower octane actually will perform better.
as to your link to the response from Lexus, that was a very softly worded response that meant nothing to me. It's exactly what I would expect to support their "requirement".
As as far as why they would recommend it, that could be a variety of reasons. But as long as I believe the Lexus and Toyota engine are identcial other than minor differences in the exhaust system, which I do believe they are, then I really don't care what Lexus reason is.
as to your link to the response from Lexus, that was a very softly worded response that meant nothing to me. It's exactly what I would expect to support their "requirement".
As as far as why they would recommend it, that could be a variety of reasons. But as long as I believe the Lexus and Toyota engine are identcial other than minor differences in the exhaust system, which I do believe they are, then I really don't care what Lexus reason is.
#193
The fuel grade posts on CL are exhausting long reads no matter where you look. Use what you are comfortable with and move on..Enjoy!
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vansprink (06-06-19)
#194
Driver School Candidate
i was told about the buying of 2 grades from a gas station offering 3 grades from an owner i met also . this is in the northeast though , i wouldn't know where else this happens .