I know this is an old thread, but for info for folk like me who are researching the topic 93 octane is NOT always better than 87. Lower octane fuel actually is more volatile and contains a bit more energy than higher octane fuel. (Read more power and MPG all else being equal.) The reason high performance engines make more power is their higher compression ratio extracts more energy from the fuel than a lower ratio will and more than makes up for the lower energy due to the higher octane. Therefore, a higher compression ratio on higher octane (but lower energy) fuel can make more total power than a lower compression engine burning lower octane (but higher power) fuel. A higher compression ratio is a big factor in causing detonation. Detonation will destroy any engine, sometimes with amazing rapidity. Higher octane is more resistant to detonation, which is why it is recommended in engines with higher compression ratios.

 

In MY car... Premium ethanol free = night and day difference.
I used to be cheap until i tried it.
As i now get better milage it pays for itself

 

Ditto

 

Lower octane actually has the potential for better mpg. The reason most suffer reduced mpg when using lower octane is because they don't keep their foot out of it - when opening the throttle a good ways and the cylinder is filling up to more of it's potential it creates the condition where it is more susceptible to detonation. The knock sensors then retard the ignition timing to prevent that detonation. Retarded ignition timing seriously degrades mpg, enough so to more than make up for any mpg gain from the lower octane. So if you drive your car very mildly, you will rarely need premium octane fuel and will likely see increased mpg. However, if you often drive a bit more aggressively, the above scenario will occur and you will definately notice reduced performance and mpg.

Many people don't realize that the octane requirement of their car varies greatly at different points in their trip based on how much engine power they are using.

Engine damage can and will happen when detonation occurs regularly. However, vehicles equipped with knock sensors retard the ignition timing to prevent that from happening.

 

I can only speak for my own car, 2.5 with a small head shave.

My wife filled it with 87, from empty. She got less than a mile from the station; had to have it trailered. At the shop, put it on the computer. At idle, it was close to the limits of the ECM, any throttle at all, it went beyond the limits, and the engine went into limp.

Gas was tested (vendor and and indy) and was well within spec.

Drain and refill with our usual 93/no alcohol, detonation sensor almost never fires; 93 with alcohol never hits the sensor...but I get measurably better mileage with the non ETOH fuel. This makes sense, since the alcohol mix, although it makes a bit less power also runs just slightly cooler.

The car will run fine on 91, just a bit less mileage. It will get you there and back on 89, but performance is crappy, and mileage sucks.

Again, literally, your mileage may vary...but remember that I have another almost half-point of compression over stock.

And, yes, everything from 87 through 91 use the same base 87 stock, 93/94 is a different stock (more isooctane), which is blended with the 87 to make the midgrades.

93 is probably overkill, but for a dime a gallon, I'll take the slightly better mileage, which pretty much breaks it even.

What DOES make a difference is what brand of gas you use; different brands use different additive packages, most times the gas comes from the same refineries! (In my corner of the world, you are getting gas, 90% of the time, from Valero or Sunoco, regardless of who the actual vendor is). My van could care less what it gets, the Jag likes Shell and Citgo.

 

I was wondering about the "ethanol free" 93 octane. I've heard it's better, but why?
There's only one station that sells it where I live and it's a bit out of the way. Is there a real advantage?

 

I'm sure that the following will set off yet another debate but-

1) E10 fuel contains 3% less energy than pure gas. Expect a corresponding minor reduction in mileage.

2) Cars built in the early 90s onward are fully compatible with ethanol levels of up to 10% concentration. There's no credible evidence of any damage being done, just a lot of scaremongering.

If you were at a given gas station and had the choice of E10 or pure gas with no difference in price, then pure gas would be the logical choice for the 3% better mileage. If you have to drive out of your way or the pure gas is more expensive, forget it.

Your car also does not need 93 octane, E10 or otherwise. Jag certified the car to achieve full performance on 91. Higher octane than that is just wasted money.

Let the arguments begin...................

 

I've driven 75000 miles in this x type
Always used 87-91 depending on circumstances, 91 always ran better, with a better throttle response.
Couple months ago tried ethanol free 91 oct. it felt like a new car.
Yes, it may have been any of the above posts reasons, but my experience beats any strangers posts... RAN LIKE A NEW CAR!.
Yes, maybe the engine is about to explode or die but my kitty likes the pricey stuff.

 

Also keep in mind that ethanol's ideal fuel air ratio is far richer than gasoline. So in the old days of carbs, 10% ethanol fuel would mean the engine would run slightly lean. Not sure if the oxygen sensor and mapping will correct the ratio when running ethanol or not nowadays. Ethanol up to 10 % won't corrode modern day fuel systems but any higher ratio requires specialized parts to handle it without corroding.

 

It's 3% richer. Modern EFI engines adjust automatically. Older engines are almost always fall on the rich side so even a 3% change makes little difference.

 

I agree, Mikey, that is exactly what I find.

The biggest difference in the non ETOH fuel is that you don't have all of the winterizing garbage in it; Winter E10 is more like E15.

91 still works in my car, but that 11.2 CR versus the 10.8 makes a difference!

I miss the old days...my Buick lived happily on 110/120 LL Blue...but that was 12.5:1 with iron heads! Used to drain it out of the wing tanks and put fresh stuff in the plane...helluva lot cheaper than Cam2 or Sunoco Blue!

To E10's credit...the alcohol mix does delay detonation better than straight gas.

 

E10 Gas has a shelf life of only 3 months.

Gas Expiration - Ethanol Blend Fuels Have a Short Shelf Life
Ethanol alcohol fuel blends have a shelf life of only 90-100 days, under ideal environmental conditions.
When exposed to water, E10 gas will contaminate and should be discarded.
Only 1 tablespoon of water/per gallon will cause fuel to contaminate/separate!
Replace gas in your fuel tank every 2-3 weeks to avoid alcohol and water related engine problems. Monitor and Test gas for alcohol and water content frequently.
Several factors affect the shelf life of ethanol blend gasolines...
Gasoline blends without ethanol, have a shelf life of many years. The shelf life of E10 is lower due to ethanol's affinity to attract and absorb water.
The public has not been properly educated in the changes in fuel system management since the switchover to alcohol blends of fuel.
Even many gas stations owners, do not realize that E10 is expired (bad fuel) only after about 90 days from the date ethanol was added to the gasoline. Often when tanks are not properly serviced before switching to ethanol blends of fuel, the water present at the bottom of tank will immediately contaminate the new E10 gas added.(most underground tanks, contains at least 2" of water at the bottom and is considered acceptable)
All gas supplied to the public contains preservatives - But this preservatives and stabilizers do almost nothing to prevent water contamination.
Foolishly, many consumers are adding extra "additives" to their gas tanks that sometimes deceptively claim they will prevent ethanol water absorption - No product/additive with this capability exists.
Several additives/products may help with the undesirable side effects, due to ethanol chemical properties (drying agent, solvent, etc.) -
No product exists that will prevent water absorption by alcohol.
All alcohols have a natural affinity for water. By nature, they attract and absorb moisture.
Whether or not the alcohol is in a medical, cleanser, beverage or fuel - All alcohols attract water.
It's the "water absorbing" properties that makes ethanol gas most problematic and difficult to manage.
- Petroleum does not blend with water.
Therefore, when excess water enters fuel supply, gasoline will phase separate.
- Phase-separated gas is contaminated and should never be used in engines.
Not only does separated fuel create obvious problems, (E.G. poor performance and release of water into engine) when phase separation of the water level is introduced into engine; Water in fuel distorts the hundreds of other ingredients that gasoline contains.
- Water-contaminated and phase-separated fuel will experience a drop in octane.
- Ethanol gasoline is hygroscopic (will absorb water) and can absorb 50 times more water than conventional non-alcohol gasoline.
Phase separation occurs in E10 gas, when only 0.5% water or 3.8 teaspoons water per gallon of fuel is absorbed.
At 70 degrees Fahrenheit, conventional (non-alcohol) gasoline can dissolve up to 150 parts per million (ppm) water. The situation is different for gasoline oxygenated with 10 % volume ethanol...

Phase Separation
With the process of phase separation, two layers of liquid are visible. An upper ethanol-deficient gasoline layer and a lower ethanol-rich (up to 75% ethanol) water layer. It occurs because ethanol is completely soluble in water but only marginally soluble in hydrocarbons...After phase separation, the gasoline layer will have a lower octane number. The fuel also is less volatile.




Precautions
When using fuels that contain alcohol/ethanol, special precautions are necessary to prevent contamination by water.
The amount of ethanol blended in at the pumps, is not closely monitored.
The ethanol is not added at the major refineries - Usually it is the delivery truck driver who adds the ethanol to fuel supply. (Now there's a guy you can trust...NOT)
Checking that gasoline meets safe and legal alcohol guidelines (10% or lower), seems recommended, until more stringent and protective laws are passed.
Refilling often, with high quality, fresh gasoline, is the best measure you can take to manage the shorter shelf life and higher risk of water contamination that occurs when using E10 and other alcohol fuel blends.

Remember; E10 Gas has a shelf life of only 3 months.

You can draw your own conclusions, but I prefer not to drive around with watered down fuel, especially in my JAG.

 

There is some good info in what you've posted but this part, when put in such absolute terms, is utterly false.....



There are simply too many variables involved.

And what defines "shelf life"? The period of time before some amount of degradation occurs? Or the period of time before the fuel is clearly unsuitable for use? If the former, I strongly suspect non-E10 will suffer degradation after 90-100 as well. If the former, well, I've had no problem with 2 year old E10 gasoline. In one case a Corvette with 4 year old E10 fired right up...although I'll admit in that instance the engine wasn't very happy about it.

As the caretaker of a privately owned collection of classic/exotic/special interest cars I can say that E10 gasoline has posed no particular or unique problem in the long term storage of cars....at least not under the conditions my employer's cars are stored.

It is extremely popular....certainly in the world of old car hobbyists.... to summarily blame any fuel related problem on E10. This comes up all the time in my conversations with others. When asked "How do you know that the problem you're having is actually, specifically related to E10 fuel?" I've yet to get anything but a blank stare in response. They're just jumping on the E10 whipping-post band wagon.

This is not to say that problems related to E10 can't occur. They can.

As for running E10 on a daily basis, well, in my neck o' the woods E10 has been standard issue for at least 20 years. If all the horror stories... as told by the hand-wringers and fist-shakers.... were actually true the sides of the road would be strewn with broken down cars. But, they aren't.

The whole E10 thing has been ballyhooed and exaggerated totally out of proportion....worse even than the sky-is-falling hullabaloo we had to endure when lead was removed from fuel 40 years ago.


Cheers
DD

 

Didn't you get the email? Ethanol is SATAN!


Just a few days ago in a separate thread I was (incorrectly) accused of plagiarism. Seems that now the accuser is guilty himself.

J'accuse!

Gasoline Expiration - Ethanol Blend Fuels Have a Short Shelf Life

What a hoot. What's worse is the pilfered text is from a website that's trying to peddle hokey merchandise to the uninformed. Classic snake oil techniques. Hardly a credible source.

Similar to Doug's experience, I've been using E10 for twentyish years in all my toys. Never had a moment's problem.

 

Hey, I'm sorry I asked!!

 

Can't we get on to more important things, like how much better synthetic oil is compared to dino oil......or is it the other way around? I always forget.

 

According to most chefs, extra virgin olive oil is the best.

 

When I stated ethanol I meant methyl alcohol - not gasahol. Of course, alcohol's ratio is around 5 or 6 to 1 while gasoline is 14.7 to 1. It could make a bit more difference than 3% when the ethanol/gasoline ratio goes over 10% - BP used to be famous for that - heard it had been tested and found at 15% methanol and have heard all sorts of horror stories about BP gas. I just never bought gas a BP and still don't.

Another thing to mention is it can be wise to buy fuel from a high volume station. It then stands to reason the fuel will be fresher and will likely have less water absorption.

I have heard that Citgo uses fuel that is 2 octane points higher than what is stated on the pump for each grade. That was some time ago so I don't know if it still holds true today.

 

I figured since you do it all the time..I might as well do it too..But I never implied these were my words except for the last sentence...Only an FYI article and not trying to jam my thoughts down anyone's throat like you do by talking your smarter than thou rhetoric.

Yer like a mosquito, take a hike Mike.

 

E10 is strictly ethanol. Not methyl alcohol/methanol.

No retailer I know of blend their gasoline with methanol.