Octane requirment for a 1993 4.3LX

[SpoMonte]

Hi,

I'm new to boating. I have a 1993 Dolphin Gemini 199 CC which has a 4.3LX. No manual was provided so I question what the required octane level is. Does anyone know what the manufacturer recommends?

Thanks,
Nick

 

[Rick Stephens]

87 will run fine. I have always run 92 octane in Idaho because it is ethanol free. I expect I would notice no difference on 87 octane except the added maintenance for ethanol's hydroscopic tendencies..

 

[Bondo]

Ayuh,.... I have run plain ole Regular, til ethanol free gas became available, which is the only gas I buy now a days,.....

 

[SpoMonte]

87 will run fine. I have always run 92 octane in Idaho because it is ethanol free. I expect I would notice no difference on 87 octane except the added maintenance for ethanol's hydroscopic tendencies..

Is hydroscopic tendencies only an issue when fuel sits for a period of time?

 

[Rick Stephens]

Is hydroscopic tendencies only an issue when fuel sits for a period of time?

Is only a problem whenever water is present. Water and ethanol are solvents to each other. When they come into contact they mix, period, whether sitting or freshly filled. Once mixed the gunk created falls out of suspension (phase separation) and the octane level of the gas drops a bunch.

Here's a well written paragraph I dug up:

For marine engines, gas with 10% ethanol or less is recommended. Ethanol fuel in boat motors can put a quick damper on your weekend plans. One of the unfortunate characteristics of ethanol is that it attracts and absorbs water. Gasoline with ethanol can absorb roughly 10 times as much water and still burn through the engine. However, when water comes in contact with ethanol blended fuel, the fuel and water can separate to form distinct layers in your tank. The upper “gasoline” layer will be depleted of ethanol and have a reduced octane level. The lower “phase separation” layer will be a corrosive mix of water and ethanol and no chemical agent or fuel additive can be added to E10 gasoline, in a reasonable quantity, that will fully prevent phase separation or recombine a phase-separated layer. An engine won't run on the water-soaked, highly corrosive ethanol solution that sinks to the bottom of the tank.

 

[SpoMonte]

Is only a problem whenever water is present. Water and ethanol are solvents to each other. When they come into contact they mix, period, whether sitting or freshly filled. Once mixed the gunk created falls out of suspension (phase separation) and the octane level of the gas drops a bunch.

Here's a well written paragraph I dug up:

I knew there was a problem, just didn't know how bad it was.
Thanks for the info!

 

[Scott06]

I knew there was a problem, just didn't know how bad it was.
Thanks for the info!

If you burn through it regularly its not an issue -really only a problem when it sits. We have a boat and a jet ski. I always fill the boat with 92 octane non ethanol, because thats all the local marina carries and i don’t feel like lugging cans for 30 gal fill ups. Conversely the ski i fill with 10% ethanol 87 pump gas , never had an issue. Two water craft kept at the end of the same dock, two different fuels no issues, cause they get used often and the fuel doesn’t sit (Stabil before winter lay up)