6 gallon portable tank...and water

[gran398]

My jon boat has a 25 Johnson 3 cyl. After Christmas it started running bad. Took it in, new power pack.

Went to crank it last night to go flounder gigging. Wouldn't crank. Took it back in this morning, mechanic was nice enough to check it out while I was there.

Drained the carbs...looked like yellow cream coming out of the carbs. Goop and water.

The mechainic says plastic tanks leak water....In a heavy rain, water gets in through the cap and vent. Not just a little water either...we sucked the water out of the bottom with a pump...There was half a gallon of water at least.

He advised to turn a coffee cup upside down on the cap from here out.

[GoneFission]

So is the little Johnson running good again?     That 3 cylinder 25 horse is a great mota!  

[gran398]

Yep brother, she's running like a champ. Glad we found the issue...I swore given its age I wasn't going to spend any more money on it...so whew! Miss D about broke me anyway

Come on over, we'll go get some for the freezer

[fitz73222]

Here is an interesting experiment that may be pertinent. I recently needed to replace my old outboard test tank for a new one. About a year ago, I brought home a brand new plastic drum from work. It was completetly drained of its contents and resealed. I kept the drum outside, upside down with bungs down. It was exposed to sun, heat, cold etc. I went to move it the other day to make my new test tank and it had about 3 gallons of water in it! I was amazed that because of the thermal cycling that this drum sweated that much water from condensation. No reason to think it can't happen to a 6 gallon tank of boat fuel sitting in the sun day after day. My advice Scott, is to keep the fuel tank in the garage at a more stable temperature and preferably with the vent closed.

[gran398]

You hit the nail on the head. Because that tank sits in the boat, exposed, every day.

To further pursue this....what's to stop this cycling in a below-deck poly tank? Or for that matter, an aluminum tank? Is poly more susceptible to moisture formation?

[wingtime]

You hit the nail on the head. Because that tank sits in the boat, exposed, every day.

To further pursue this....what's to stop this cycling in a below-deck poly tank? Or for that matter, an aluminum tank? Is poly more susceptible to moisture formation?

Keep the airspace in the tank to a minimum...  by keeping it full of fuel!  Or keep it empty.  Those are your options.

[Capt. Bob]

poly more susceptible to moisture formation?

If you understand the process of moisture formation then think of materials that are good at heat transfer. The same materials are also good conductors of electricity.

[gran398]

poly more susceptible to moisture formation?

If you understand the process of moisture formation then think of materials that are good at heat transfer. The same materials are also good conductors of electricity.

I'd like to think I do...but honestly I don't. Your observations before on poly...we gained from your input.

Let's take this forward....tell us your thinking here

[Capt. Bob]

poly more susceptible to moisture formation?

If you understand the process of moisture formation then think of materials that are good at heat transfer. The same materials are also good conductors of electricity.

I'd like to think I do...but honestly I don't. Your observations before on poly...we gained from your input.

Let's take this forward....tell us your thinking here

Take Fitz's "drum". He doesn't state the size but let's pretend it's a 55 gallon container. If the drum contains no fluid and he seals the drum completely at a known temperature and pressure (let's say, 80 degrees F. and @ sea level) then we can determine how much water vapor is present in the enclosed drum. Through rain, sleet, hail, heat of day, and dead (think cold) of night, his faithful drum sits in his backyard. What happens inside is defined. There is just so much water vapor available to change from gas to liquid unless the drum has a way for water vapor to enter. In his example, his drum (unless it's way bigger than 55 gals) will need a way to recharge the atmosphere within with more vapor.

Now think of a fuel tank. Completely empty or half full, it still contains space for air. In our example we will state that the air has water vapor in it (cause it does). You have a way for water vapor to enter (and leave) the tank via the venting system. So as the existing vapor changes state (condenses) new vapor can (and does) take its place. Over time, this "cycle" continues and water continues to condense in the tank. If the tank were completely sealed, this would still happen but would be limited to the amount of water vapor present when the tank was sealed. With our type of fuel system, sealing doesn't work real well so we need to vent the system so it will function.

Now on your question about poly tanks vs, aluminum. First, let's reiterate what we know from everyday living here in the south. Its that warm air can hold more water vapor than cool air. Humidity, if I remember correctly is the difference between how much water vapor is present in the air and the level of vapor the air can hold before being saturated (think rain). This may not be the true definition but you get the idea. Here in Fla. we experience high levels of humidity and so there is a good deal of water vapor present in the air.
Now there are several ways to change the physical state of the water vapor (gas to liquid). You can continue to add vapor to the air until it reaches a level of saturation and can no longer hold it in a gaseous state or you can alter the gas (in this case plain ol' air) either by changes in pressure or temperature. Either will affect the air's ability to retain water vapor in the system.

So, during the day, your tank sits in the sun warming the air inside gathering that vapor laden air through the vent. Now night comes and the air temps fall. This in turn lowers the surface temp of your tank. You asked about poly vs. aluminum. As I stated, you need to understand which material is a better heat transfer (aka conductor) material. Example, beer cans are made of aluminum, coolers are made of plastics. Inside your electronics or your computer you will see a "heat sink" on sections that get hot. The back of your VHF radio should have one also. It's not poly. So, your poly tank will provide just a bit more insulation to the air inside the tank and will delay condensation a little longer. Remember, as the heat in the air is transferred to the colder surface of the tank wall, it's ability to retain the water vapor  is diminished and it changes it's physicals state (from gas to liquid) This is the basic engineering principle  (heat transfer) of air conditioning and stills.

So aluminum is an excellent conductor of electricity and heat transfer. Poly, not so much. Doesn't mean the tank won't sweat but it's less likely in the same circumstances.  Take it out of the boat and put it inside. Keep it filled to reduce air space and thus water vapor. Drink a beer.

All work equally well.

[gran398]

That was great Bob!

Thank you  

[wingtime]

Add ethanol into Capt Bob's scenario...  Water is soluble in ethanol... in fact it almost has an appetite for water!  So during all those cycles the ethanol in the fuel itself is just absorbing the water.  Unlike non ethanol gas where the water is NOT soluble the droplets would show up as bubbles in the bottom of the gas.  In ethanol the water is absorbed and you can't see it!  That is until it reaches the saturation point and the water/ethanol mixture separates out of the gas.  At that point it will look like salad dressing!  YUMMY!

[gran398]

That is exactly right!!

When we drained the carbs....this chit that looked like mayo dribbled out.

"Nah...its just a little ice cream"

 

[GoneFission]

No, it's just a little ice cream:

http://www.youtube.com/watch?v=UO9A4p1Qsvk

[Blue Agave]

Back to the flounder Scotty. I'm from Missouri, show me!

[gran398]

I sure wish you boys down there could go gig you some doormats. It's like taking candy from a baby.