trentor

So it seems that many places in Arkansas and Oklahoma are proudly advertising "No Ethanol" in their gas. I think most would agree this is a great thing since ethanol has been found to be hard on engines and is less efficient than gasoline.

So, the morning of the BMT I posed a question to many...which is better? 91 octane with no ethanol or 93 octane with the common E10 or E15 mixture. The answer from every. single. person was the 91 with no ethanol.

That morning I actually had filled up with the 93 w/ ethanol, but at lunch as well as in OK on my way home Sunday, I topped it off with 91 and no ethanol. So very much to my surprise, my car absolutely ran like crap. My ECU very obviously was compensating and my retarding timing or something at lower rpms. At higher rpms it wasn't so noticeable, but from about 1700-3000 rpm I had less power and absolutely horrible pinging. If it was just one fill-up, I'd possibly write it off as bad gas, but this was from two different stations in different states.

As soon as I got home and filled her with the usual QuikTrip 93 w/ ethanol, she runs like a champ again. Now, I don't know enough to know whether it really has anything to do with the ethanol or not, but I don't recall this problem the other (few) times I've used 91.

Thoughts?


On a related note, make sure to read this website if you're not familiar with it. The list of retailers might surprise you. http://www.toptiergas.com/

pmptx

I didn't notice a great difference, however it may just be a Nissan thing
Interesting that Exxon Mobil is not on the top tier list. Looks like QT it is.

Thanks for polling folks. the OK forum actually has a running list of the all gas no ethanol stations in the OK AK LA areas, so it is certainly a hot topic.

altiain

Your original question is a bit misleading. You’re trying to compare two separate variables.

91 octane fuel is 91 octane fuel, regardless of ethanol content. Same goes for 93 octane. The octane rating is a measure of the fuel’s resistance to detonation and is independent of the chemical composition of said fuel.

If your car was designed to run on 93 octane, it will retard timing and make other changes in order to prevent detonation with 91 octane fuel, again, regardless of ethanol content. These changes will effectively reduce engine output by some degree, and different cars are affected differently. This is why you felt that your car was low on power while running on the 91 octane fuel. The culprit behind the power reduction was the octane rating of the fuel, not the ethanol percentage.

Where straight gasoline and blended gasolines (like E10 or E15) differ greatly is in fuel economy. Since ethanol has a lower heating value (unit of energy per unit mass) than “straight” gasoline, fuel economy is inversely related to ethanol percentage. The higher the percentage of ethanol in your fuel, the lower your observed fuel economy will be, all other things being equal.

Gernby

I haven't had any problems with any gasoline I've ever bought.

I believe toptiergas.com is sort of a scam, IIRC. I think it's just a site that sells a spot on their list for money.

Elistan

Well, considering I've never heard even a single anecdote of somebody having to replace fuel system or engine parts due to damage from E10... and I assume if that ever happened in the online automotive community we'd hear all about it... that's an aspect I'm not worried about.

Which leaves the energy-content-per-unit-volume question altiain talks about. (We're not too concerned about per-mass, my friend, that's for the NASA boys. ) And since ethanol is actually replacing another oxygenate, MTBE, which made up 15% of gasoline when it was used - a gallon of gasoline with 10% ethanol has nearly the same energy content as a gallon of gasoline with 15% MTBE.

Base gasoline : 114,000 BTU per gallon.
E10 : 0.9*114,000 + 0.1*76,100 = 110,210 BTU per gallon.
MTBE : 0.85*114,000 + 0.15*93,500 = 110,925 BTU per gallon.

So those of us who have been using oxygenated fuel for a while haven't seen any significant mileage change with the switch to E10.

Now obviously there's less energy than in a gallon of gas. So I'd take pure 93 octane gasoline over 93 octane E10 any day. But for my high-compression, 9000-rpm engine - I'd take 93 over 91, period.

Gernby

Actually, one of the track junkies did an E85 build, and quickly had his stock rubber fuel lines come apart.

Elistan

^^ Thanks. I've edited my post to reflect what I meant when I said "ethanol" - E10. Ethanol in sufficient quantities absolutely will cause damage.

altiain

Mark has way too much free time on his hands today, I think.

Absolutely - you'll see little difference in fuel economy between MTBE-oxygenated (often referred to as “reformulated”) fuel and E10. However, outside of smog pollution counties you can often get non-reformulated gasoline, which provides significantly better mileage than E10 or MTBE-oxygenated gasoline.

Gernby

I have no idea what I've been getting at the QT near my house in Collin County. How do you know what type of gasoline you're getting? Are there supposed to be stickers on the pump? The last time I looked, I think there was just a sticker saying something like "This gasoline may contain up to 10% Ethanol".

altiain

If you live in Collin, Dallas, Tarrant, Ellis, or any of the other smog countied in North Texas, than your gasoline has 10% ethanol by law.