Gas for my 2003 Utopia with 250 optimax

[Daniel D]

Around here I can only find 91 octane ethanol free fuel.

My service manual asks for 87 octane. I've read plenty of things on other forums about not running higher octane in my optimax.

So my question is... Is it better for my Optimax to run 91 octane ethanol free or 87 octane with 10 percent ethanol?

 

[Dr Honda]

There's a couple schools of thought... but here's the deal.....

1) Octane is a measure of fuel ignition and/or burn speed. (pressure changes the speed too) So... when the piston comes to the top of the stroke, it's ignited. Ideally, you want that fuel to all burn just as the exhaust valve is opened. (in the case of a 2-stroke, as the port is exposed) If the fuel is still burning as the exhaust opens... first... you aren't extracting all the potential power from the fuel... and second... all that hot, burning fuel rushes past the edge of the piston, and cyl port. That concentrates the heat in that zone... and COULD potentially melt the piston crown. (So, melted engine) Also, it's wasted $$$ since the performance is actually lower with "Premium" fuel in your engine. You can re-tune the engine to take advantage of the 91... but that would require the compression to be raised.

So that's why you REALLY shouldn't run it in your engine. BUT....

2) Some people have really issues with our new "Oxygenated" (alcohol) fuels. They can cause issues with the rubber parts in the fuel system... and the alcohol attracts water. When water does get in... you can get a phase separation, and that just makes a mess in the fuel tank that needs drained.

These are real issues, and real concerns. But with that said... I don't have issue with modern fuels. I simply keep a good shot of fuel stabilizer in my boat/PWC tanks... and it's NEVER been a concern. the Marine "Stay-bil" works as it should, and I've even burnt a couple tanks of fuel that were well over a year old, because my XP800 has a tendency of sitting. Also... the fuel parts in the Mercury boats are OK with the alcohol. (Early Seadoo PWC rotted the fuel lines)

AND... the last point on the modern fuel is... the alcohol actually supports more HP because it's combustion is more stable, and burns slightly cooler.

To me... there are more positive with new fuels over the negative.

SO... burn 87 to 89 octaine, keep fuel stabilizer in the fuel... and don't worry about looking for, and going out of your way to get alcohol free fuel.

My 2 cents... take it for what it's worth.

 

[Daniel D]

Wow, thanks for the very detailed response. It is much appreciated

 

[Daniel D]

If you're using the boat regularly and going through a tank of gas each week would you still user stabilizer?

Or just when you're gonna leave it sit for awhile?

 

[Dr Honda]

Absolutely ! Part of the problem with the new fuel is water. If you get enough in there... the water doesn't just go to the bottom (and get sucked into the filter) the extra water is what starts the phase separation. SO... keeping stabilizer in there will keep that issue in check. Not to mention... with a boat... you never know when the weather will shift, and the boat will sit. I, myself have used my boat WAY less than I wanted to this season. It keeps raining, and the rivers are full of junk.

 

[Daniel D]

Again, thanks for sharing your knowledge. There have been quite a few days this summer we've been waiting for smoke to clear from forest fires before we want to go out. We could use a bunch of that rain!

 

[jasguild]

the Marine "Stay-bil" works as it should, and I've even burnt a couple tanks of fuel that were well over a year old, because my XP800 has a tendency of sitting.

Out of curiosity how much Marine stabil do you use?

 

[Dr Honda]

Generally, the recommended amount on the label. If you mean... how much over all.... on a busy sumer, I will use one of the "big" bottles. All water toys get some with every fill up... and all my stuff gets it before going to bed for the winter. (motorcycles, ATV's, and lawn equipment)

 

[jasguild]

the label says 1 oz for every 10 gallons. when I go to the gas station, I usually put in about 15 - 20 gallons. I usually dont fill to the max because it always end up spilling gas even when I try to listen and be careful. that amount of gas usually puts the fuel gauge at full even though I am not sure how close it is to being full.

so I have been use 2 ounces of marine stabil on the premise that I am adding approximately 20 gallons and the previous gas in the tank was already treated.

Regarding your suggestion about dealing with ethanol, I agree that Stabil is the most cost effective and convenient way to deal with gas. I only have one gas station in my neighborhood that sells ethanol free gas and the corners in the gas station are tight to navigate a boat and trailer through.

 

[Dr Honda]

................

so I have been use 2 ounces of marine stabil on the premise that I am adding approximately 20 gallons and the previous gas in the tank was already treated.

.........

Sounds about right to me.