I’ve been in and on outboard driven boats with internal fuel tanks all my life. Worked as a b iologist at Ft. Johnson for ~ 7 years… and never saw this happen. But, having seen it now, I thought it was worth passing on.
I filled up my 17’ HenryO a few weeks back, brought it home and parked it in its place, bow up and cover on. On the first good warm afternoon, I got home from work to a strong gasoline odor which quickly led me to the gas vent on the boat. Gas was slowly dribbling out of the vent and down the side of the boat onto the drive. I immediately opened the fill cap and pressure rushed out and the vent quit dribbbling.
Best I can figure, I got the tank full enough that when I raised the bow (trailer jack), the vent hose connection on the tank was submerged. The warm afternoon caused the vapor space to expand and push fuel up and out the vent line. It lokked like a couple of quarts made it out.
Just a cautionary tale. My driveway and side of the boat presented a real fire hazard. I’m glad the was no ignition source.
Now, I raise the bow just enough to make her drain rain, and no more.
17’ Henry O Hornet
26’ Palmer Scott
Funny, I had the same thing happen last Summer. I also had completely filled the tank. I try not to completely top it off anymore.
The ethanol gas is good enough reason to keep 'em empty nowadays anyhow.
Glad no sparks were around!
There’s two schools of thought; keep the tanks full or keep them empty. Personally, I believe in keeping them full. Water gets into the tank as water vapor in the air. The less air that is in the tank means less water. If you have an empty tank the daily temperature flucutation will cause condensation. Then when you fill up, the ethanol bonds with it.
I’ve never had more that two drops of water in my separating filter in three years.
Iain Pelto
Edgewater 185CC “Jumpin’ Bean II”
Native Manta Ray 14
Hairball, I agree with you. Even with ethanol/gas, I try to keep the tank full. If you are using eth/gas, it comes out of the underground tanks with a compliment of moisture. The more you add (allow to occur), the more likely you are to get phase separation. Keeping the tanks nearly full minimizes the addition of more moisture, thus slowing the impending phase separation.
As I understand it, the phase separation happens when you reach a certain concentration of H2O in the eth/gas mixture. Anywhere below that concentration, you don’t get phase separation and the H2O gets blown through the motor as usual. Any gasoline (ethanol or not) has some moisture in it. As long as the concentration stays low, it stays in suspension is not a problem. It is only when the concentration exceeds a certain point that it drops out. Ethanol doesn’t change that dynamic much… it just brings along a little extra moisture to make the separation happen more quickly.
Are there any chemical engineers out there that can confirm or refute this?
17’ Henry O Hornet
26’ Palmer Scott
How about pulling the fuel line and letting the lines to the carbs run completely out of gas? Would that help or would the residue left from ethanol still do the same amount of damage?