Fuel octane degradation 9 months sitting

[1978elcamino]

Our two Seadoo's sit on a lift on the water. Last year I put them on the trailer mid September because of Hurricane Helene, then came Milton. While they were off the lift I did the annual service and filled them completely to the top with 89 octane ethanol free fuel from Wawa, thats the only fuel they have ever had.
The lift was damaged from the hurricane and the Ski's will probably be back on the lift and ready for use in May.
The Ski's are not supercharged and do not require premium. Seadoo recommends 90 octane and pretty much every fuel station in florida is either 89 or 90 octane if you buy ethanol free.
Question is, the fuel will be about nine months old by May. Should I use an octane additive or send it. IDK, never have let anything sit unused for 9 months.

 

[The motor guy]

Our two Seadoo's sit on a lift on the water. Last year I put them on the trailer mid September because of Hurricane Helene, then came Milton. While they were off the lift I did the annual service and filled them completely to the top with 89 octane ethanol free fuel from Wawa, thats the only fuel they have ever had.
The lift was damaged from the hurricane and the Ski's will probably be back on the lift and ready for use in May.
The Ski's are not supercharged and do not require premium. Seadoo recommends 90 octane and pretty much every fuel station in florida is either 89 or 90 octane if you buy ethanol free.
Question is, the fuel will be about nine months old by May. Should I use an octane additive or send it. IDK, never have let anything sit unused for 9 months.

You have any 5 gallon cans? I'd siphon some out like half of it and then fill up with some fresh fuel, then add the old gas back in. That's the problem with filling it up all the way, but imo it's probably fine assuming it runs good. Don't waste your money on octane boosters. When they say a 3 point improvement, usually that means .3

 

[SubieRubyRoo]

When they say a 3 point improvement, usually that means .3

Points = tenths of a number; read as “plus point 3”
Numbers = whole number improvement; read as “plus 3”

 

[1978elcamino]

is there a "rule of thumb" calculation of how long it takes for octane to be reduced if properly stored in a garage?

 

[shortyb]

Was the fuel stabilized? I'd be more worried about other constituents aging from the lay-up than octane. Like any other small engine, they may be real sensitive to fuel. Drain the gas and put it in your car and fill the toys up with fresh fuel is my recommendation.

 

[The motor guy]

Points = tenths of a number; read as “plus point 3”
Numbers = whole number improvement; read as “plus 3”

Just what I heard on here. They get sneaky with it

 

[1978elcamino]

Was the fuel stabilized? I'd be more worried about other constituents aging from the lay-up than octane. Like any other small engine, they may be real sensitive to fuel. Drain the gas and put it in your car and fill the toys up with fresh fuel is my recommendation.

They are used frequently and filled to the top with fresh ethanol free fuel. So, stored properly? I suppose yes since they have been in the garage for 9 months.

 

[shortyb]

They are used frequently and filled to the top with fresh ethanol free fuel. So, stored properly? I suppose yes since they have been in the garage for 9 months.

Send it.

 

[tnt_motorsports]

our extended family has the opposite from you. The ski's and boat sit from April or May to November without use due to the Snowbird affect. They are stored with Wawa rec fuel and stabilizer. Not an issue firing them up in the years I have been there to do it in the fall... If the fuel was stabilized, I'd send them. If not then try it and if they stumble or don't run well at the dock or on the lift, empty and refill. You could connect your flush line and let them run for a bit to see if they start easy.

 

[kschachn]

Was the fuel stabilized? I'd be more worried about other constituents aging from the lay-up than octane. Like any other small engine, they may be real sensitive to fuel. Drain the gas and put it in your car and fill the toys up with fresh fuel is my recommendation.

Me too. The fuel octane rating isn’t what I’d be worried about, if I was worried about anything.

 

[1978elcamino]

Me too. The fuel octane rating isn’t what I’d be worried about, if I was worried about anything.

Oh well heck, I store 6 gallon fuel jugs with ethanol free 89 in my garage for sometimes close to a year.
Once huricane season is over and its too cold out for using the boat or Ski's I put that fuel in my truck.
I just dont want to worry about any octane related damage caused by low octane preignition in the Ski's.
If you have ever been on a pwc you cant really hear much on the water let alone spark knock.

 

[shortyb]

Are they 2 or 4 strokes? 2 stroke I would definately be concerned about low octane knock, especially if they are really high compression. 4 stroke wouldn't be as concerned. They probably have more sophisticated electronic ignition systems, quite possibly with knock sensors.

 

[1978elcamino]

they are 4 strokes, 170hp 3 cylinder rotax engines

 

[1978elcamino]

NA 1,630 cc 3 cylinder 11:1 compression ratio with knock sensors.
The standard marina fuel is 90 octane ethanol free and that is what most people run in them, even the supercharged engines.
They use A LOT of fuel, there is nothing efficient about jet propulsion. Many times we go out for the day leaving with full tanks, 18 gallons I think, we still have to go to a Marina and fuel up. So they have plenty of fresh fuel run through them 8 months out of the year.

 

[SubieRubyRoo]

Are they 2 or 4 strokes? 2 stroke I would definately be concerned about low octane knock, especially if they are really high compression. 4 stroke wouldn't be as concerned. They probably have more sophisticated electronic ignition systems, quite possibly with knock sensors.

Nothing over 9.5:1 2-strokes made any sustainable improvements in power, and were detrimental in knock results that resulted in piston erosion and increased heat load on the piston, increasing the risk of micro-welding or popping piston tops off. Low-compression 2-strokes with properly-tuned exhausts is where they are happiest and most successful; this has been known for many decades now.

https://www.bridgestonemotorcycle.com/documents/higher_compression6.pdf

 

[shortyb]

Nothing over 9.5:1 2-strokes made any sustainable improvements in power, and were detrimental in knock results that resulted in piston erosion and increased heat load on the piston, increasing the risk of micro-welding or popping piston tops off. Low-compression 2-strokes with properly-tuned exhausts is where they are happiest and most successful; this has been known for many decades now.

https://www.bridgestonemotorcycle.com/documents/higher_compression6.pdf

Indeed. My sadly departed 03 RIVA Stg. 2 GP1300R was punched out to 1390 (long stroke, undersquare) and I was constantly measuring squish to keep compression a hair over 9:1. Had quite the collection of head gaskets in a variety of thicknesses. Big torque that thing had. My water partner threw a high comp head on his XP and then wondered why he soon ate a set of real nice Wisecos. Proper 2 stroke tuning is Voodoo science at it's best .

 

[The motor guy]

NA 1,630 cc 3 cylinder 11:1 compression ratio with knock sensors.
The standard marina fuel is 90 octane ethanol free and that is what most people run in them, even the supercharged engines.
They use A LOT of fuel, there is nothing efficient about jet propulsion. Many times we go out for the day leaving with full tanks, 18 gallons I think, we still have to go to a Marina and fuel up. So they have plenty of fresh fuel run through them 8 months out of the year.

This is why I recommend getting atleast half the fuel out and refueling with 93 octane.