Another Gas question...

[JoeSki]

I apologize if this one has been covered before, aside from changing the oil and plugs, my engine knowledge is minimal.

I have a '98 sport Nautique w/ GT-40. The motor calls for 89 octane, which I have been using with stabil and have never had a problem.

My family and I recently moved and the gas station near our house has a non-oxygenated pump, its 91 octane though.

So....what would be better, 89 octane with stabil or non-oxygenated 91 octane?

[Nautiquehunter]

Higher octane is better . Does it have ethanol in it?

[DanielC]

Higher octane is not better, it is just higher octane.

Octane in simple terms is a measure of how fast the air fuel mixture burns in the cylinder, after the spark plug fires. Higher octane burns slower.

There is a point, somewhere slightly after the cylinder has passed TDC, that the engine wants maximum cylinder pressure, from the burnt fuel and air. Running a higher octane than required makes the maximum pressure occur slightly later. It is the same effect as retarding the ignition timing slightly. You cannot change the ignition timing on a GT-40 engine, the engine's computer controls the ignition timing. In fact, the engine's computer, with the knock sensor can change the ignition timing to accommodate a lower octane gas.

What do you do with your boat? If you are a barefooter, or use it for slalom skiing, I would be a little more concerned about getting at least 89 octane gas. Same if you use the boat for wakeboarding, with lots of ballast. If you use the boat for just cruising around, without towing anything, the fuel requirements are not as critical.

How long does the boat go between fillups? if you only fill the boat every month or so, continue to use Sta-Bil. If your choice is limited to 87, or 91 octane, consider the use, as I described above, and choose what you want.

[JoeSki]

Thanks for the info Daniel

We mostly slalom ski with our boat and the frequency of fill-up varies, we rarely fill over 1/2 a tank for weighting/ wake reasons (not sure if that makes a difference?).

We never run anything less than 89 octane, but my thought was...would 91 octane non-oxygenated and without ethanol be better than 89 octane with ethanol?

[DanielC]

I have been running 89 octane E-10 in my boat (1997 Ski Nautique, 2270 hours) since about 1998. I have not had any problems from the alcohol in the gas.
I do try to keep my tank pretty full. I live in Oregon, and we do not have the humidity that is common in the Midwest.

If you have not been running E-10 until now, it could cause a problem, if you have much water already in your gas tank.

[Nautiquehunter]

DanielC
I'm not following your statements. Are you saying using 91 in a stock engine will cause a performance problem? Can engine damage occur by using 91 over the 89? Is 91 non ethanol worse than using 89 with ethanol?

[TRBenj]

DanielC
I'm not following your statements. Are you saying using 91 in a stock engine will cause a performance problem? Can engine damage occur by using 91 over the 89? Is 91 non ethanol worse than using 89 with ethanol?

No, it shouldnt cause damage- there isnt a huge difference between 89 and 91 octane. But an engine that isnt designed for higher octane will not perform any better with it... so all else being equal, its a waste of money. If you were talking 100+ octane race fuel, then the answer may be different... in that case, the difference in recommended octane is quite large and may cause an issue with both performance and damage on an engine not designed to take advantage of it. Ive never gotten a very good answer on that question.

The ethanol content is a totally separate issue. I would be inclined to pay a little more for non-ethanol fuel, especially if the gas was going to sit in the tank for a while (winter storage, etc). If youre going to burn the gas relatively quickly (within a few weeks) then it doesnt make much difference.

[shag]

I am not an Ethanol fan. I do believe however, that the Ethanol related problems are more prevalent in high humidity locations (Florida for example). I agree with TRBenj, if you are using your boat often, the E10 might not be an issue, but for those that don't use as often, I would try to use non-ethanol. There was a bill recently (last year) that has surfaced in Florida to try and get rid of Ethanol based fuels here, or at least make regular non-ethanol fuel more readily available, and give consumers a choice at the pump. I know we need to decrease our independence on foreign oil, but when it is to sacrifice damaging fuel system components and also make your car less efficient..... Not sure the status of that bill right now.
I did a little experiment last year. I compared my mileage with E10 to 2 tanks of non-ethanol fuel. (since I have been using E10 always, I used two tanks to be sure that all the E10 was used up.) Same driving conditions/weather/time of year/same average routes/driving habits/etc. With the E10 I averaged about 13mpg (07' GMC Sierra). With the non-ethanol I averaged about 16mpg. This is per the vehicle computer and via my own mileage calculation. I could actually see a difference in the 'instant mileage' readout on the dash. To me, that is significant. This was by no means a scientific study, lol, but I literally drove mostly the same routes, no idling except at lights, highway speeds of about 70mph when able to. Problem is here is that the only station with non-ethanol is about 30 miles away and it is about $4/gallon. I have a gas dock that I fill occasionally and use that for mowers,etc.
I had a 05' San 210 3 years ago that had a fuel pump problem, surging at different times. When I took it in for service, they found the 'sealed' fuel pump inside the FCC was completely corroded! To the point that they could not even believe it was working at all. It was just outside of the warranty, but PCM stepped up and warranted it anyway (great customer service!), but PCM said that it was due to using the E10 fuel (I'm guessing that with the condensation here due to the humidity, there managed to be a bit of moisture in the tank, over time, the E10 must pull the moisture into the pump, and then it caused the damage) There are times when the boat is used every week, but other times that it might sit for several weeks, covered, in a boathouse on a lift, with vents and damp rid). I know some people have had no issues at all, but I have plenty of reasons to NOT like E10 fuel. IMO
Have a great day!

[JoeSki]

Thanks for the good info guys! If I am hearing everyone, the 91 octane will not cause issues with the GT-40.
I think I will be inclined to spend a little more on the 91 octane non-ethanol gas, especially since it is so close to the house.

[madcityskier]

The higher the ethanol rating, the higher the cumbstion point. Therefore, less premature ignition, and more fuel to create the explosion to drive the cylinder. This results in a trade of smoother and greater power, for higher fuel usage and temperature. Generally using a higher octane fuel than the engine calls (within reason)for will be a waste of fuel but not usually a notable amount of extra wear on the engine. If the engine doesn't run right on the correct fuel, start with a tune up.

[AirTool]

The higher the ethanol rating, the higher the combustion point.

Can you elaborate on this one?

[TX-Foilhead]

Ethanol raises the octane level, but you get less energy from burning it. If you had a motor designed and tuned to run E85 all the time you might get more out of it. They don't design them that way though, hey are tuned to run every grade of gas so you just end up with a mediocre tune that doesn't excel with any grade.

Running something without ethanol would most likely cut the fuel consumption enough to pay for the extra cost of a higher grade especially on a motor not designed to run ethanol. When I got my F150 ethanol was rare, I could get 19+ mpg on trips, these days the best I ever seen is 17 if I run a whole tank on the highway. If I put E85 in I won't get more than 12, there is absolutely no savings to run that crap even though I can. I do it once a year for cleaning purposes only.