# Wrong Fuel Type



## Thisiseasy (Aug 3, 2017)

I'm on a vacation and drove my car, a Chevy Impala, to upper Michigan. I cannot find E85 gas anywhere and had to fill up at a rural gas station this evening because I was on empty. They only had 91 gas. I drove 30 miles to get back to where we're staying and nothing bad has happened yet.

Did I just screw up my car?


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## XSleeper (Sep 23, 2007)

Just because a car can run on E85 doesn't mean you can ONLY run it on E85. 91 octane is fine, the computer will adjust to it. If it was the other way around, you would not want to put E85 in a car that is not designed to burn it. Not all cars are flex fuel. Yours is, apparently.


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## ron45 (Feb 25, 2014)

My pickup truck can run on E85 but I only use 87 octane with 10%.


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## CodeMatters (Aug 16, 2017)

Read the owners manual. Quite certain you'll find that less/no ethanol is fine. E85 
is a maximum (amount of ethanol), not a minimum. Also it might be fine to run on
regular 87. If so, buying 91 is a waste of money.


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## CaptTom (Dec 31, 2017)

Thisiseasy said:


> ...I cannot find E85 gas anywhere...
> 
> Did I just screw up my car?


No, you found a good place to buy fuel!

E85 is an overall "worse" fuel than normal gasoline, by just about every measure.

The only reason it's sold at all is it's mandated by law in some parts of the country. I won't talk about why, otherwise we'd have to move this to the political forum.

And very few cars need 91 octane. High octane is not "better" fuel, it's just that some very high-compression engines need it. Normal engines don't, and don't run any better with it.


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## Bigplanz (Apr 10, 2009)

Even vehicles that require (according to the manufacturer) 91 octane will run on 87. The computer in the vehicle will retard or advance the timing to compensate for a knock condition. My Navigator requires 92 octane but I have always put 87 in it and it runs fine. I suppose if I towed something, the higher octane would be needed, but just running around town the performance of the engine is fine. 

Never heard a ping or knock even when I floor it to get on the Watterson Expressway (Bumper sticker frequently seen here before it was widened: "Pray for me, I drive on the Watterson Expressway." It is still pretty bad, but it used to be horrible. 45 degree up angle on ramps, 20 feet of merge lane, everybody driving 70 and you're in a chevette.... the bad old days!!)


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## chandler48 (Jun 5, 2017)

I find, too, that location has a great deal to do with gas. We use 87 octane here in the South, but when visiting my daughter in Denver, their norm is 91 octane, no lower.


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## lenaitch (Feb 10, 2014)

chandler48 said:


> I find, too, that location has a great deal to do with gas. We use 87 octane here in the South, but when visiting my daughter in Denver, their norm is 91 octane, no lower.


Interesting. I wonder if that has something to do with the elevation. Although the air is ultimately compressed, the intake sensors would be reading a lower density air. Dunno.


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## Oso954 (Jun 23, 2012)

It’s actually the other way around. The lower air density reduces your need for octane in a normally aspirated engine.

The last time I was in Denver (quite a few years ago), they sold 3 grades. Regular was 85 octane, mid was 87 and premium was 91. At the same time, lower elevation stations in other states only offered the 87 regular and 91 premium.

Things may have changed since then, IDK. But I find 91 octane as the norm (regular?) a bit hard to believe.


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## SeniorSitizen (Sep 10, 2012)

The hi octane is to prevent detonation at higher elevations. The guys that run the Pikes Peak race can answer your questions.


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## chandler48 (Jun 5, 2017)

My apologies, I went the wrong way with my figures. I added rather than subtracted. Their norm is 85 octane while ours is 87. And yes it has to do with the elevation. We once drove a Southern based F150 to Rifle Co. to do some hunting. Although we were using local gas, we barely made it up Eisenhower Pass. The computer couldn't acclimate fast enough. Once through the tunnel we pulled over for about 20 minutes and continued on.


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## Oso954 (Jun 23, 2012)

My guess is the non acclimating has nothing to do with octane. The computer is supposed to be reducing the fuel charge based upon the air mass reduction with altitude. If it’s not acclimating, you are running to rich. That’s going to rob a lot of power.

In the old days, I used to down size my carb jets before leaving for the mountains. It cost me a little power down low, but the Car performed better at altitude.


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## chandler48 (Jun 5, 2017)

No, it didn't. We were using local fuel. The computer was apparently just not adjusting fast enough. It lived its life at 1500' above sea level. Throw in 11,000' and it blew its mind.

I had a Jeep Renegade CJ5 with the 302 V8. I removed the stock exhaust and put tuned headers on it with Hush Thrush exiting aft of the door. Engine would absolutely not run due to lack of back pressure. I had to do major dawdling with the carb to get it to behave right. Ran better and better fuel mileage afterwards.


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## Thisiseasy (Aug 3, 2017)

So, E85 refers to the amount of ethanol in the fuel, whereas 91 refers to octane? I did read my handbook and it does say that anywhere from 85% ethanol to 0% ethanol is acceptable.

The gas station that's closest to my cousin's place only has one type of fuel available to purchase and it's 91. I used it twice now and nothing bad has happened. Actually, I have noticed the gas mileage improve significantly.


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## CaptTom (Dec 31, 2017)

Thisiseasy said:


> So, E85 refers to the amount of ethanol in the fuel, whereas 91 refers to octane? I did read my handbook and it does say that anywhere from 85% ethanol to 0% ethanol is acceptable.
> 
> The gas station that's closest to my cousin's place only has one type of fuel available to purchase and it's 91. I used it twice now and nothing bad has happened. Actually, I have noticed the gas mileage improve significantly.


Correct.

You should notice a significant improvement in mileage. Some say possibly up to 10%, but I haven't done the math.

Ethanol has less energy content by volume. It's also less volatile, so it increases the "octane" rating number (without actually adding any real octane.) All the "octane" rating really means is the fuel's resistance to pre-ignition ("knock"). A higher number doesn't necessarily mean a "better" fuel, just a less volatile (and in the case of ethanol, a less efficient) one.


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## polychrome (Oct 4, 2013)

Bigplanz said:


> Even vehicles that require (according to the manufacturer) 91 octane will run on 87. The computer in the vehicle will retard or advance the timing to compensate for a knock condition. My Navigator requires 92 octane but I have always put 87 in it and it runs fine. I suppose if I towed something, the higher octane would be needed, but just running around town the performance of the engine is fine.
> 
> Never heard a ping or knock even when I floor it to get on the Watterson Expressway (Bumper sticker frequently seen here before it was widened: "Pray for me, I drive on the Watterson Expressway." It is still pretty bad, but it used to be horrible. 45 degree up angle on ramps, 20 feet of merge lane, everybody driving 70 and you're in a chevette.... the bad old days!!)


 There are car's from the 90's and earlier with higher compression ratios that won't run well on 87 octane, the engine controller is forced to run rich to prevent knock and they get reduced power and fuel economy and it tends to cook the catalytic converter. 

Lower NOx tailpipe emission limits forced auto makers to reduce NOx formed during combustion which requires keeping the peak cylinder combustion temperature and pressure below a specific point, which means using a lower compression ratio. Lower compression ratio also reduces the octane rating required to prevent detonation, as well as the maximum achievable thermodynamic efficiency of the engine and HP per cubic inch, but not much and there are more promising ways to boost mileage and HP than going back to high compression ratios and 100 octane fuel.


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