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Old 03-23-2010, 03:53 PM
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Question What happens if you use 87 octane gas?

Hey guys,

I know we should be using 91 octane gas but I was just asking what happens if you run with 87?

The main reason I'm asking is because right when I got the car I put in 87 for about a month before I realised I was supposed to be using 91... What kind of damage could it have caused and what should I do to try and reverse any of that damage?

I use 91 now but I was just wondering if theres anything I should do to clean it out or something?

Thanks a lot
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Old 03-23-2010, 03:58 PM
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The ecu will retard timing and lower power for low octane gas.



The worst that could have happened was your plugs may have fouled out, but if it drives okay, you're probably fine. Don't worry about it, just keep using 91.
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Old 03-23-2010, 04:04 PM
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Lol one time the station was out of 91 or 93 so I had to use 87 to get me to the next station and My check engine light came on and car drove like pure hell
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Old 03-23-2010, 04:07 PM
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Yeah the car drives fine now. When I was using the 87 octane I noticed that the car sometimes had trouble turning over but ever since I swapped to 91 the car runs super smooth.

My other question is that where I live the 3 types of gas are 87,89 and 91...Is 89 good enough or should I really use 91?
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Old 03-23-2010, 04:09 PM
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use the highest octane possible. 93 would be the best (reasonably).
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Old 03-23-2010, 05:01 PM
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You'd only save about $1.50 for 89 instead of 91, why even bother?
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Old 03-23-2010, 05:02 PM
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Use whatever octane gas the cars engine is built for and the ECU is programmed for.

The octane rating only dictates how hard the fuel is to ignite, it does not dictate the quality of the gas. 87 is easier to ignite than 89, which is easier to ignite than 91, etc.

If you run higher octane than your cars engine and ECU are meant (what it's properly built and tuned for) to use, the engine will have trouble igniting the fuel: your fuel mileage will go down, you will lose power, and it will generally run worse (although it won't be greatly noticeable if the octane difference is small).

If you run lower octane than your cars engine and ECU are meant to use, your engine may pre-ignite the fuel which can severely damage the engine. This happens when pressures inside the cylinder are high enough to ignite the fuel before the spark plug actually fires (ie high rpm or high boost [or both] situations).

The moral of the story is run what the car is built for. Our cars are built for 91 (at least in California, it may be 93 in other states).
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Old 03-23-2010, 05:07 PM
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we have pretty good knock sensors so detonation isn't a huge issue, but yeah, run what it was designed for.

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Old 03-23-2010, 05:34 PM
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Thank you Mr. Education.

Run 93 and you'll be happy.
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Old 03-23-2010, 06:58 PM
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i used 87 for my S4 and it ran fine and my brothers A4 was fine too
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Old 03-23-2010, 07:03 PM
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I've always run 93 in mine, just cause its easier to find around here than 91. Either way, your motor should be fine.
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Old 03-23-2010, 07:42 PM
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Well like I said the highest we have where I live is 91 so I'll just use 91. Thanks for all the info.
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Old 03-23-2010, 08:06 PM
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Quote:
Originally Posted by pyropenguin View Post
we have pretty good knock sensors so detonation isn't a huge issue, but yeah, run what it was designed for.
Knock sensors can only detect knock that is already occurring. If the ECU detects it, it can turn on the safety maps (at least on most cars) and run in limp mode, but it doesn't prevent knock from happening in the first place. Your engine knocking a little bit (if the fuel pre-ignites once, or a couple times) probably won't cause any damage, but if it happens again and again the probability it will cause damage goes up.

At stock power levels, running 87 "probably" won't hurt your engine, but, as everyone else said, it's always best to run what it's designed for.
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Old 03-24-2010, 09:42 AM
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^^yep. If $1-3 more per tank is gonna break you, sell your Audi
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Old 03-24-2010, 03:23 PM
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^^lmao
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Old 02-23-2013, 03:33 PM
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Default MPG Octane Averages

I have tried all octanes with my 2007 a3 and kept track of average mileage for each fuel type. I discovered something rather interesting:

91 octane yields 24.3 mpg
98 octane yields 23.9 mpg
87 octane yields 21.6 mpg

Verdict is in. I guess higher octane pays for itself.
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Old 07-28-2014, 01:00 AM
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hello, has anyone here used 87 gas on a regular basis for their A4 and actually had long term engine problems?
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Old 07-28-2014, 04:24 AM
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Here in Aussie Land, we have

91 Octane with 10% ethanol.
95 Octane
98 Octane

I have always used 98 octane even though it is more expensive as I have found that it provides more power and on a very hot day, it is much less likely to ping!
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Old 08-12-2014, 03:43 PM
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Quote:
Originally Posted by turtleboy View Post
Use whatever octane gas the cars engine is built for and the ECU is programmed for.

The octane rating only dictates how hard the fuel is to ignite, it does not dictate the quality of the gas. 87 is easier to ignite than 89, which is easier to ignite than 91, etc.

If you run higher octane than your cars engine and ECU are meant (what it's properly built and tuned for) to use, the engine will have trouble igniting the fuel: your fuel mileage will go down, you will lose power, and it will generally run worse (although it won't be greatly noticeable if the octane difference is small).

If you run lower octane than your cars engine and ECU are meant to use, your engine may pre-ignite the fuel which can severely damage the engine. This happens when pressures inside the cylinder are high enough to ignite the fuel before the spark plug actually fires (ie high rpm or high boost [or both] situations).

The moral of the story is run what the car is built for. Our cars are built for 91 (at least in California, it may be 93 in other states).
well said. I try to explain this to ppl all the time and they look at me like im the dumb one. if you car calls for 91 for example, running a higher octane wont give them more power, it will actually reduce power and lower you gas mileage.

but you know ppl's way of thinking, higher octane=more power. guess what, hivher octane has less BTU's which in turn is less power.
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Old 08-14-2014, 12:01 PM
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Quote:
Originally Posted by GrapeBandit View Post
well said. I try to explain this to ppl all the time and they look at me like im the dumb one. if you car calls for 91 for example, running a higher octane wont give them more power, it will actually reduce power and lower you gas mileage.

but you know ppl's way of thinking, higher octane=more power. guess what, hivher octane has less BITU's which in turn is less power.
I don't think the previous post was all that accurate though. The Octane rating has nothing to do with how hard fuel is to ignite. It's a comparison to the anti-knock properties of the hydrocarbon Octane, which is considered 100. All gasolines are a blend of various hydrocarbons, and release similar energy when burned. Also, people often confuse pre-ignition with detonation. Higher Octane reduces the tendency to detonate, not pre-ignite. Higher Octane likewise won't affect the fuel mileage while cruising either.

By the way, when I used to fly Cessnas and fill them up with 100LL gas at the airports, I'd also fill my turboed car and sportbike with that too. Higher boost and smelled great too.
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