switching from 87 octane to 89 octane gas (IS250)
#46
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Join Date: Feb 2012
Location: New Jersey
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I totally disagree with the 87 is a devil if dealer requires premium. Until this car i never filled up super. My e39 530i and my 05 Legacy GT turbo all required premium gas. None of those cars knocked ever, nor did i ever have issues because of the gas i was using. As far as gas mileage i never saw an increase or felt the power difference on WOT. Even on the legacy WOT seemed the same! I am not sure why i decided to use premium for this car only but this is what it is. Also when i took loaners from lexus, i only put 87 in those cars, when i had is350 loaner that car felt just like mine no difference on 87.
#47
Lexus Test Driver
Running 87 is not "perfectly fine"
The engine, ECU, etc are all designed to run on premium for optimum performance. That's why there's a sticker that says to use Premium fuel.
They didn't put it there for giggles.
Running 87 will just reduce performance as the knock sensor kicks in and the car compensates for the lower octane fuel. Probably not good at all long term for the motor either...
The engine, ECU, etc are all designed to run on premium for optimum performance. That's why there's a sticker that says to use Premium fuel.
They didn't put it there for giggles.
Running 87 will just reduce performance as the knock sensor kicks in and the car compensates for the lower octane fuel. Probably not good at all long term for the motor either...
#48
Lexus Fanatic
iTrader: (1)
I totally disagree with the 87 is a devil if dealer requires premium. Until this car i never filled up super. My e39 530i and my 05 Legacy GT turbo all required premium gas. None of those cars knocked ever, nor did i ever have issues because of the gas i was using. As far as gas mileage i never saw an increase or felt the power difference on WOT. Even on the legacy WOT seemed the same! I am not sure why i decided to use premium for this car only but this is what it is. Also when i took loaners from lexus, i only put 87 in those cars, when i had is350 loaner that car felt just like mine no difference on 87.
Because if not then you have no idea if they ever knocked.
This isn't a 70s pinto where you can obviously hear and notice when the engine is knocking.
Knock sensors and ECUs are very good anymore. They'll hide it extremely well.
It doesn't mean it's never happening.
I actually have datalogged in cars, including ones tuned for higher octane fuel (including cars I've tuned myself too)... and the knock happens even if you don't notice it. (and you generally never do- as I say, modern cars are really good about catching it and pulling timing)
Now, if you don't plan to keep the car more than 50-100k miles, and aren't racing it, you probably don't give a crap... (other than you are likely to get provably more power and better mileage with the fuel the car requires, but it'd take more than "feeling" to prove it- you'd need to datalog under controlled conditions for more than 1 or 2 tanks, and if not racing you won't miss the extra ~10 hp or whatever)
I mean, there's literally no motivation at all for a car maker to "require" a higher octane fuel than the car actually needs... cheaper fuel would be a selling point... so it's not like they're saying you need premium for their benefit.
#49
Lexus Test Driver
iTrader: (1)
Kurtz,
I have never data logged my 250. I do have access to one, I may do it one of these days.
My question is this, you are claiming 87 octane will knock. Do you have data logging to prove it? Because I am not seeing a loss of power.
From my understanding, the o2 sensor measures heat of the exhaust, and leans and richens the mixture as needed. If the vehicle is knocking wouldnt that change the exhaust heat?
I have never data logged my 250. I do have access to one, I may do it one of these days.
My question is this, you are claiming 87 octane will knock. Do you have data logging to prove it? Because I am not seeing a loss of power.
From my understanding, the o2 sensor measures heat of the exhaust, and leans and richens the mixture as needed. If the vehicle is knocking wouldnt that change the exhaust heat?
#50
Lexus Test Driver
Kurtz,
I have never data logged my 250. I do have access to one, I may do it one of these days.
My question is this, you are claiming 87 octane will knock. Do you have data logging to prove it? Because I am not seeing a loss of power.
From my understanding, the o2 sensor measures heat of the exhaust, and leans and richens the mixture as needed. If the vehicle is knocking wouldnt that change the exhaust heat?
I have never data logged my 250. I do have access to one, I may do it one of these days.
My question is this, you are claiming 87 octane will knock. Do you have data logging to prove it? Because I am not seeing a loss of power.
From my understanding, the o2 sensor measures heat of the exhaust, and leans and richens the mixture as needed. If the vehicle is knocking wouldnt that change the exhaust heat?
"The sensor does not actually measure oxygen concentration, but rather the difference between the amount of oxygen in the exhaust gas and the amount of oxygen in air. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess."
http://en.wikipedia.org/wiki/Oxygen_sensor
Because we know the concentration of oxygen molecules in our atmosphere it makes it rather easy to determine.
It doesnt measure heat....otherwise they'd probably call it a heat sensor.
#51
I totally disagree with the 87 is a devil if dealer requires premium. Until this car i never filled up super. My e39 530i and my 05 Legacy GT turbo all required premium gas. None of those cars knocked ever, nor did i ever have issues because of the gas i was using. As far as gas mileage i never saw an increase or felt the power difference on WOT. Even on the legacy WOT seemed the same! I am not sure why i decided to use premium for this car only but this is what it is. Also when i took loaners from lexus, i only put 87 in those cars, when i had is350 loaner that car felt just like mine no difference on 87.
In my experiment with 89 mid-grade I specifically limited my driving to light throttle, mostly highway cruising and cooler temperatures in winter. These conditions made it less likely for the engine to knock, so I could get away with using 89 octane and my mileage was the same.
#52
Kurtz,
I have never data logged my 250. I do have access to one, I may do it one of these days.
My question is this, you are claiming 87 octane will knock. Do you have data logging to prove it? Because I am not seeing a loss of power.
From my understanding, the o2 sensor measures heat of the exhaust, and leans and richens the mixture as needed. If the vehicle is knocking wouldnt that change the exhaust heat?
I have never data logged my 250. I do have access to one, I may do it one of these days.
My question is this, you are claiming 87 octane will knock. Do you have data logging to prove it? Because I am not seeing a loss of power.
From my understanding, the o2 sensor measures heat of the exhaust, and leans and richens the mixture as needed. If the vehicle is knocking wouldnt that change the exhaust heat?
#53
Lexus Fanatic
iTrader: (1)
seems a couple other folks have already addressed most of the questions for me (and quite well too) but I'll just mention no I have not datalogged an IS250 on 87 octane specifically... the reason I'm saying it will knock eventually (esp if driven hard at all) is because for one that's the only reason it would say "Requires 91 octane fuel" several places on the car and owners manual.
Otherwise the requirement would make no sense and actually hurt sales of the vehicle because it "needs" more expensive gas.
And as explained, it's mainly ignition timing (combined with engine compression) that's causing the requirement- the timing is programmed to work properly with 91, and if it doesn't get it it will eventually knock and retard the timing.
Or you can just read the PDF Toymota attached, which explicitly states the car will retard timing on lower octane fuel (and goes into some detail about it)
Otherwise the requirement would make no sense and actually hurt sales of the vehicle because it "needs" more expensive gas.
And as explained, it's mainly ignition timing (combined with engine compression) that's causing the requirement- the timing is programmed to work properly with 91, and if it doesn't get it it will eventually knock and retard the timing.
Or you can just read the PDF Toymota attached, which explicitly states the car will retard timing on lower octane fuel (and goes into some detail about it)
Last edited by Kurtz; 06-11-12 at 07:18 PM.
#55
Pole Position
iTrader: (2)
Truth vs. Fact. If you want truth, read some Nietzsche. Facts on the other hand are based on scientific principals.
http://www.differencebetween.net/mis...act-and-truth/
It is a fact that your engine will run better on 91 octane.
BTW, the O2 sensor and the knock sensor are just that, sensors. These sensors do not directly change mixture or engine timing, they are inputs to the ECM. The ECM controls mixture and engine timing.
http://www.differencebetween.net/mis...act-and-truth/
It is a fact that your engine will run better on 91 octane.
BTW, the O2 sensor and the knock sensor are just that, sensors. These sensors do not directly change mixture or engine timing, they are inputs to the ECM. The ECM controls mixture and engine timing.
#57
Driver School Candidate
I run 91 in my car but here's some info i picked up from car talk not sure if its valid or not on our cars You need to run lower octane gas in higher altitudes if you have carburetor otherwise you risk damaging your engine for some reason. Mountain states carry 85 gas because of this.
When i had my G35, i noticed a big difference in gas mileage when filling up in Vegas with non ethanol gas. Used to be able to get MTBE gas in California buts that changed 10 years ago. I assume the reason for this is that ethanol has less energy for volume than gas but it has higher octane, its around 100 octane. Also my G35 owners manual stated notto use any gas with ethanol in it but that was kinda hard living in California which banned MTBE.
When i had my G35, i noticed a big difference in gas mileage when filling up in Vegas with non ethanol gas. Used to be able to get MTBE gas in California buts that changed 10 years ago. I assume the reason for this is that ethanol has less energy for volume than gas but it has higher octane, its around 100 octane. Also my G35 owners manual stated notto use any gas with ethanol in it but that was kinda hard living in California which banned MTBE.
#58
Lexus Test Driver
iTrader: (1)
Thanks for the link! This explains how the ECU learns a persons driving habits and stores it in memory, and adjusts engine timing as need be for optimal performance.
I am happy with the performance, mpg of my 250. Would it run better on higher octane? Of course it will! But, I have logged 110k miles with out any issues (knock on wood) so I will continue to use it.
#59
Lexus Fanatic
iTrader: (1)
I run 91 in my car but here's some info i picked up from car talk not sure if its valid or not on our cars You need to run lower octane gas in higher altitudes if you have carburetor otherwise you risk damaging your engine for some reason. Mountain states carry 85 gas because of this.
And I don't think any major car maker has even made carburated cars in the US in over 20+ years at this point