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      07-26-2021, 03:09 PM   #1
jpy1980
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Question on Octane Used on my Wife's Car

So I leased my wife a 2019 Audi Q7 3.0T back in 2019 for a 3 year period.

Now for all of MY cars, I treat them better than my first born, but since this was a lease and we decided we would definitely re-lease a new car at the end, I decided to use 87 octane instead of the recommended 91 octane. I know, I know. Bad bad cheap me. BUT now that the car has served us so well, my wife wants to keep it. UGH. The car drives fine and I have followed the maintenance schedule, but have I done any real harm? How could I check and see if it's worth keeping? I'm usually the type of person that even treats rental cars well, but with this car I just didn't think it was worth it since we weren't going to keep it.

Thoughts?
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      07-26-2021, 03:20 PM   #2
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you're probably fine. the ecu will adjust for the 87. if the car was driven like a grandma i wouldn't worry. if you're wife has a heavy foot and redlines it often.. i'd maybe look for another car.
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      07-26-2021, 03:21 PM   #3
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The ecu just compensated for the lower octane so I'd assume it didn't cause any damage but who knows long-term. If there haven't been any CEL then I'd say it's fine.

Talk about karma biting you back in the ass lol.
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      07-26-2021, 03:27 PM   #4
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That car's ECU is smarter than anyone's first born. All using 87 did was retard the timing under extreme conditions, and she never even noticed. Had you used 93 in it from day 1 it wouldn't be any better of a car. Buy it.
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      07-26-2021, 03:29 PM   #5
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Quote:
Originally Posted by VisualEcho View Post
That car's ECU is smarter than anyone's first born. All using 87 did was retard the timing under extreme conditions, and she never even noticed. Had you used 93 in it from day 1 it wouldn't be any better of a car. Buy it.
exactly !

What always cracks me up is when folks put 93 in a vehicle designed for 87, total waste of $$
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      07-26-2021, 03:30 PM   #6
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Did you use Tier 1 gas? If so, you're fine. Like any DI motor, you'll likely benefit from a carbon cleaning somewhere in the 60-100k mile range, but likely no worse than if you'd kept it on 93.
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      07-26-2021, 03:35 PM   #7
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Quote:
Originally Posted by Red Bread View Post
Did you use Tier 1 gas? If so, you're fine. Like any DI motor, you'll likely benefit from a carbon cleaning somewhere in the 60-100k mile range, but likely no worse than if you'd kept it on 93.
Yea I always used Shell as it is nearest to me.

Do you think I should run those gas treatment additives?
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      07-26-2021, 03:38 PM   #8
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Quote:
Originally Posted by jpy1980 View Post
Quote:
Originally Posted by Red Bread View Post
Did you use Tier 1 gas? If so, you're fine. Like any DI motor, you'll likely benefit from a carbon cleaning somewhere in the 60-100k mile range, but likely no worse than if you'd kept it on 93.
Yea I always used Shell as it is nearest to me.

Do you think I should run those gas treatment additives?
Nope, with direct injection they just go right out the tailpipe anyway.
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      07-26-2021, 03:50 PM   #9
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Quote:
Originally Posted by jpy1980 View Post
Yea I always used Shell as it is nearest to me.

Do you think I should run those gas treatment additives?
Run E-85 and crank up the boost!!
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      07-26-2021, 04:18 PM   #10
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My wife & I both had '16 IS200 leases that called for 91/93 octane. We ran them both with only 87 the entire lease and never had an issue.
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      07-26-2021, 04:34 PM   #11
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I'd flush the fuel tank and replace all the fuel lines, pumps, injectors, and every component which touches fuel.
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      07-26-2021, 05:07 PM   #12
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Quote:
Originally Posted by FC4 View Post
I'd flush the fuel tank and replace all the fuel lines, pumps, injectors, and every component which touches fuel.
LOL, why ??
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      07-26-2021, 07:11 PM   #13
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I agree with most of the posters...you should be fine as the ECU adjusts for the low octane level. Just a note...BMW "requires" 89 octane and "recommends" 91 octane (at least on my car).
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      07-26-2021, 07:41 PM   #14
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My wife has the same vehicle. Although she puts 91 in it all the time now, for a while she was putting 87. As most have said, the ecu will adjust but you definitely don't get the most out of that engine (supercharged V6). It was a noticeable difference which is what lead me to asking her what she had been putting in.
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      07-28-2021, 05:10 PM   #15
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Quote:
Originally Posted by mikado463 View Post
exactly !

What always cracks me up is when folks put 93 in a vehicle designed for 87, total waste of $$
Those people are great to find and sell stuff to.
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      07-28-2021, 10:58 PM   #16
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Quote:
Originally Posted by KennyFSU View Post
The ecu just compensated for the lower octane so I'd assume it didn't cause any damage but who knows long-term. If there haven't been any CEL then I'd say it's fine.

Talk about karma biting you back in the ass lol.
Plus, if the ECU retarded timing to compensate, his fuel economy probably took a slight hit, too. I don't know if it would make up the cost difference, but it would be amusing if it ended up costing the same overall.
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      07-29-2021, 11:04 AM   #17
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Americans saving 2c a gallon on gas, killin me. It's near $7 gallon here.
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      07-29-2021, 11:04 AM   #18
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Quote:
Originally Posted by chris719 View Post
Plus, if the ECU retarded timing to compensate, his fuel economy probably took a slight hit, too. I don't know if it would make up the cost difference, but it would be amusing if it ended up costing the same overall.
probably not.

did a quick calc based on info for my work truck since i drive that a lot and know pretty well what i get mpg for regular and premium, and with the current gas prices in my area ($3.50 for regular, $4.20 for premium), I have to get 3 mpg better than regular for it to break even on a cost per mile basis.

For reference, my truck gets ~17.5 mpg on 87 and ~18-18.5 mpg on 91.
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      07-29-2021, 11:08 AM   #19
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Quote:
Originally Posted by TheWatchGuy View Post
probably not.

did a quick calc based on info for my work truck since i drive that a lot and know pretty well what i get mpg for regular and premium, and with the current gas prices in my area ($3.50 for regular, $4.20 for premium), I have to get 3 mpg better than regular for it to break even on a cost per mile basis.

For reference, my truck gets ~17.5 mpg on 87 and ~18-18.5 mpg on 91.
Does your truck actually recommend premium?

Itís the high compression high performance engines, often turbo, that do.

I would wager that most people on this site have cars that recommend premium to prevent knock due to the high performance aspect of their engines, vs people that have lower performance engines that do not recommend high octane (because it doesnít do anything).
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      07-29-2021, 11:57 AM   #20
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Quote:
Originally Posted by JamesNoBrakes View Post
Does your truck actually recommend premium?

It’s the high compression high performance engines, often turbo, that do.

I would wager that most people on this site have cars that recommend premium to prevent knock due to the high performance aspect of their engines, vs people that have lower performance engines that do not recommend high octane (because it doesn’t do anything).
iirc dodge recommends 89.

heres a good comparison car and driver did. https://www.caranddriver.com/feature...dodge-charger/

I can tell you that with my BMW, i would have to get 4 mpg difference to break even with the cost of premium (tuned n54 335) and with my genesis g70, i have to get 5mpg difference to break even. Both of those recommend premium and i run premium in them. (BMW ~25mpg 91, G70 ~27mpg on 91). And i never had that big of a difference in mpg with different fuels, e85 excluded.

edit: with all that, the performance benefits and knock resistance of the higher octane fuels is worth the few cents per mile difference between the 2. in my truck, with 76k miles in 4 years, the overall cost difference if gas was the same for all 4 years is only a couple thousand $. For my other cars, with less miles and better fuel economy, its even less. like 1-2 cents more per mile
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Last edited by TheWatchGuy; 07-29-2021 at 12:07 PM..
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      07-29-2021, 01:45 PM   #21
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Quote:
Originally Posted by JamesNoBrakes View Post
Does your truck actually recommend premium?

Itís the high compression high performance engines, often turbo, that do.

I would wager that most people on this site have cars that recommend premium to prevent knock due to the high performance aspect of their engines, vs people that have lower performance engines that do not recommend high octane (because it doesnít do anything).
Yeah, although these days you never know what ECUs are working in a sort of adaptive range where they will advance timing if possible under certain conditions. It seems like some BMWs will do this if you run higher octane for a while. I wouldn't expect a Subaru base 2.5L NA engine to gain HP from 100 octane, but you never know if they benefit a little bit up to 91 or 93 despite being rated for 87.
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      07-29-2021, 11:13 PM   #22
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Quote:
Originally Posted by chris719 View Post
Yeah, although these days you never know what ECUs are working in a sort of adaptive range where they will advance timing if possible under certain conditions. It seems like some BMWs will do this if you run higher octane for a while. I wouldn't expect a Subaru base 2.5L NA engine to gain HP from 100 octane, but you never know if they benefit a little bit up to 91 or 93 despite being rated for 87.
I think in general ECUs limit the car to the rated/designed HP. This means when you put higher octane in, it "doesn't care". It doesn't try to do anything with this at all. If you have a tune, and especially if you have a turbo, you can take advantage of this, but otherwise, it just "doesn't care". The cams won't support more power and it just doesn't care.

The whole thing about "higher octane doesn't benefit" is limited to those lower performance cars and the people that buy high octane for them. My Hyundai Elantra GT N-line was specifically designed to give max performance on "regular". A little 200hp 1.6 turbo-4. With a tune and a couple mods like wastegate solenoid and boost control solenoid, I was running it on premium and it ran well, but then I was asking a little more out of it than stock. Stock, it didn't care if I put premium in or not, that's how they designed it. Cars like my SS 1LE or Stinger, they crave pretty high octane. Lower octane makes a noticeable difference.
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