Recently a local convenience store has started selling ethanol-free "boat fuel" for about 20 cents a gallon more that premium. However, it is only 89 octane. The normal premium is 93.

Which would you prefer? Why and why not?

Obviously, boost likes octane, but the ethanol-blends do bad things to cars not made for it.

I have an '06 MCS.

 

Use the 93 with E-85 and Motor On.

 

I use ethanol free as often as possible but the first requirement for your car is 91. Although your car should retard the timing and not do any damage on 89, I don't like to be running a motor relying on the safety features. I wouldn't choose to run my car on a flat run flat tire either. These safety features are to get you out of a situation, not to be an every day thing. Keep looking. You will find 91 ethanol free. Use the 89 for your lawnmowers and such. They will love it.

 

^ +1

 

Every once in a while I can hear some pinging when I'm hard on the gas....and that's with 93 w/ 10% ethanol. Not sure I would ever want to run 89 in my car....even if it's w/ 0% ethanol. Run the highest octane you can find...

 

Yep. I'm lucky enough to have a local station sell ethonal free 93 octane.

 

I don't know how current they are (with the exception of 'top tier', very current) but here's some fuel related URLs you may find helpful.
http://www.toptiergas.com/
http://pure-gas.org/index.jsp?
http://www.fuel-testers.com/state_gu...anol_laws.html
https://docs.google.com/file/d/0B5vA...U1k/edit?pli=1

 

FWIW ethanol will actually raise octane rating.

You would be better off "performance wise" running 89 with ethanol vs ethanol free 89.

As stated, there is a knock sensor, so when detonation occurs the car will pull timing to protect itself as much as it can. We've had customers run their cars on regular since purchasing them, some have had issues, others haven't. It's all in how you drive and monitor the vehicle while driving.

 

Octane is octane. By definition, ethanol free 89 gasoline has the same octane rating as a 10% blended fuel with a rating of 89, they should perform that same with regard to knock.

In the USA, all cars 2001 and newer are designed to be operated with ethanol blends up to 15% so for the OP, your car is fine using the blended fuel. Use the high octane fuel that you can find, i.e. 91 or 93. especially in the hotter months. IMHO, the yearly cost savings ($50) of the lower rated fuel is not worth the risk.

 

Exactly. Octane ratings are what they are. 89 with ethonal has the same knock level as 89 no ethonal. But ethonal has less energy output compared to equal amounts of straight gasoline. So more is required to get the same results. That's why you get better fuel mileage with non ethonal usually. Less is required to achieve the same amount of energy output. The computer uses all of its sensors and readings to adjust the fuel input and ratios accordingly.

So on a car designed to run with some ethonal you won't notice any performance difference from running non ethonal as far as power, because the computer will adjust and "inject" more fuel at a time to achieve the same performance, all you will notice is a difference in mpg.

Now vehicles running straight ethonal or E85, not to be confused with 85 octane, can run more advanced timing because straight ethonal has a higher knock resistance. Therefore more power can be made, but they suffer in the fuel mileage department. That being one reason it's not widespread for consumer factory cars, even though it's made from corn and such, meaning it's renewable.

In summary, run either. You will get same power output. Just use the highest octane rating you can find. The only benefit will be a difference in mpg.

 

There is a generic gas station near me that sells 92 octane non-ethanol premium. I always put some Techron in the tank, before I fill up, to bring it up to top tier detergent standards.

 

Thank You all for your input.

Obviously, the more octane the better. I guess I am just used to a little bit older cars (think early '90s Nissans) not liking ethanol and it doing bad things. For example, causing premature failure of fuel injectors.

I wasn't expecting any performance benefit, nor do I mind paying a little extra for better fuel. Like most have recommended, I guess I will stick with 93 and just deal with the ethanol blends.

 

you want the ethanol free if you ever need to store it a couple of months, thats why the boaters need it. ethanol sucks up moisture when it sits over the winter.

 

There's an issue never resolved with the automobile. Every pre-flight, fuel is collected from the wing tank sumps to remove/check for water which is heavier the gas. Didn't find it very often but the time or three it was, am glad it was gone instead of doing its worst from 6500 feet. Its too bad there's no way to drain it off from a car.

 

How many people do you know would be responsible enough to check that routinely on their car.....

 

It's not necessary to have it on a car. The car is not at altitude where the water can readily freeze. The engine can easily take a little water. It might cause a misfire or too but rarely any harm.

 

I run ethanol in my boat all the time....that's all I can get in my area. There is a reason why most all boats have water separator/filters on them

 

Not if you just got a little John boat fishing in ponds and lakes

 

93 here and at 260K+ miles. Sometimes 92 if the area is does not have it.

 

I can't comment on the first 122k, but the last 3k has been nothing but 93 ethonal free

 

Same number that never check the oil regularly then wonder what happened when things go badly.

 

Yep. It kills me when people are like well it was running fine and wasn't making any noises, so I changed my oil when it started to tick and now it won't go away and it's smoking a little, followed by the inevitable Craigslist ad, I'm sure it's something simple 4,000 firm no low ballers lol.

 

Your car can run a 10% ethanol blend but not E85. When you run lower octane fuel, you rely more heavily on the knock sensor and the long term adaptives to retard spark timing. Retarded spark timing leads to higher EGT's which then adds more fuel to keep EGT's down. There is certainly a greater risk of knock damage and burned exhaust valves running 89 octane than 93. A 10% ethanol blend has 3.3% less heating value than straight gasoline, so unless the fuel is 3.3% cheaper than straight gas, it's not worth it.

 

Thats why 93 oct and 260K+ later the my W10 engine is going strong