my project wellcraft 180 fisherman

[Destroyer]

The tank expands and contracts due to internal and external pressures placed on it. Gas expands much more than water in warm weather or direct sunlight, so the tank bulges as the pressure builds internally. As warm gas gets cooler it contracts, creating a lower pressure inside the tank than outside, so outside pressure pushes on the walls of the tank and gives the tank the appearance of collapsing. This also happens when an unvented tank is being used while running. As the gas is pulled from the tank by your fuel pump it creates a vacuum inside the tank and again, the external pressure of the air will push on the tank walls giving it the appearance of collapsing.

Looking at your picture I can see what appears to be a vent in the middle of the cap without the hose attached to it, where you fill the tank with gas. Open it slightly and it will release internal pressure when the gas expands due to becoming hotter, and allow external air pressure to enter as the gas cools, stopping the bulging and collapsing of the tank walls.

Like the others, I really have no positive knowledge of what that grey thing on the hose is, although it looks like a type of pressure regulator. My guess would be it's used to prevent pressurized fuel from an unvented tank squirting out of the engine end of the hose when coupling or uncoupling the hose from an engine. Early 6 gallon metal gas cans used a pressurized molded 2 hose fuel deliver system to deliver fuel to the engine. But the problem was, because it was pressurized, if there was a leak it would spray raw gas all over, creating a dangerous fire hazard. To solve that they went to a single hose with the bulb that we all know and love....but the problem with that system is if gas in the tank isn't vented, it can create pressure within the gas line, and when the hose is being attached or disconnected it can spray raw gas all over. NOT good if you are hooking up a second tank of gas to a hot engine. So I'm pretty sure that's what it is. And it's automatic, so you don't have to do anything to it. Just leave it alone and let it do it's job.

[mannydvk11]

Originally Posted by Destroyer

The tank expands and contracts due to internal and external pressures placed on it. Gas expands much more than water in warm weather or direct sunlight, so the tank bulges as the pressure builds internally. As warm gas gets cooler it contracts, creating a lower pressure inside the tank than outside, so outside pressure pushes on the walls of the tank and gives the tank the appearance of collapsing. This also happens when an unvented tank is being used while running. As the gas is pulled from the tank by your fuel pump it creates a vacuum inside the tank and again, the external pressure of the air will push on the tank walls giving it the appearance of collapsing.

Looking at your picture I can see what appears to be a vent in the middle of the cap without the hose attached to it, where you fill the tank with gas. Open it slightly and it will release internal pressure when the gas expands due to becoming hotter, and allow external air pressure to enter as the gas cools, stopping the bulging and collapsing of the tank walls.

Like the others, I really have no positive knowledge of what that grey thing on the hose is, although it looks like a type of pressure regulator. My guess would be it's used to prevent pressurized fuel from an unvented tank squirting out of the engine end of the hose when coupling or uncoupling the hose from an engine. Early 6 gallon metal gas cans used a pressurized molded 2 hose fuel deliver system to deliver fuel to the engine. But the problem was, because it was pressurized, if there was a leak it would spray raw gas all over, creating a dangerous fire hazard. To solve that they went to a single hose with the bulb that we all know and love....but the problem with that system is if gas in the tank isn't vented, it can create pressure within the gas line, and when the hose is being attached or disconnected it can spray raw gas all over. NOT good if you are hooking up a second tank of gas to a hot engine. So I'm pretty sure that's what it is. And it's automatic, so you don't have to do anything to it. Just leave it alone and let it do it's job.

really good answer thank you very much now my other Q? after that answer is if i keep it open will gas evaporate and give me water problem in my tank o will water come in the tank trow the vent also if the tank is collapse will the motor have a problem like if is running with out gas o will it prevent the gas to circulate when is collapse

https://www.youtube.com/watch?v=ewXwbDiYacM here is a link on how the gray valve is suppose to do but am not sure if this is for my motor

[Destroyer]

Originally Posted by mannydvk11

really good answer thank you very much now my other Q? after that answer is if i keep it open will gas evaporate and give me water problem in my tank o will water come in the tank trow the vent also if the tank is collapse will the motor have a problem like if is running with out gas o will it prevent the gas to circulate when is collapse

https://www.youtube.com/watch?v=ewXwbDiYacM here is a link on how the gray valve is suppose to do but am not sure if this is for my motor

Okay, one at a time...

1) If you open the vent then yes, a very tiny portion of gas will evaporate over time. Since your gas is inside an enclosed container, the only place for it to go is either out the fuel line to the engine, or (as a vapor) a tiny amount out the vent on your gas cap. The hole in the vent is very small, and only allows for expansion or contraction at a slow rate. Just enough to equalize the inside and outside pressures. As you run your engine and it pulls fuel from the tank zero gas vapor escapes from the vent. But once the engine is stopped and the gas inside starts to expand then a tiny amount of gas vapor will escape. So yes, you will lose a minuscule amount, but insignificant in the overall scheme of things.

2) No, you will not get any significant water into your tank by allowing the vent to be open during operation of your boat. Just screw the vent closed at the end of the days run. In a much larger tank, where the gas sits for days or weeks at a time, and there is not way to close the vent, then yes, due to first expansion of the gas during the warm day and then contraction of the gas during the cooler night, a small amount of water, in the form of humidity in the air will enter the tank and then condense into water as it cools. That's one of the reasons why we have fuel/water separators on the fuel line(s) going to the engine. If you still have a fear of water entering your engine from the tank, just empty whatever is left in it at the end of the day into your lawn mower. string trimmer, auto, whatever, and start out with a fresh tank of gas on your next time out on the water.

3) Yes, if the vent is closed, then your engine will create a vacuum in the tank as it pulls fuel from it. That vacuum will eventually become so strong that either the engine will stall out because it can no longer overcome the vacuum and receive gas, or, the plastic tank will collapse from the greater (14.7 lbs psig at sea level) atmospheric pressure being exerted on the outside of the tank.

Remember....NO manufacturer is going to add anything extra to a product if it isn't needed.... that costs money and will eat into their profit. So in the case of your plastic gas tank, the vent that is added into the gas cap costs the maker extra money and would not be there if it were not needed. Use it, it's there for a reason.

[mannydvk11]

thanks you very much Destroyer i was wondering about that because i saw that happen to me yesterday when i took the boat out for a run and the gas tank was collapse and the engine was turning off at hi rpms

[Destroyer]

Mannydvk11, I did a little research and found out what that grey thing is. As I suspected, it's a pressure regulation device. It's called a "Fuel Demand Valve". You can find out all about it at the following link:

http://www.mercurymarine.com/parts-a...e-fuel-system/

Please notice that in the description it clearly states that it's to prevent fuel from a pressurized tank entering an engine and creating a fire hazard. What isn't stated is that the pressurized tank is being mandated by the EPA (Extremely Pathetic A$$holes) to prevent fuel vapor from entering the atmosphere. (Even though pressurized tanks create a fire hazard). In other words, it's something that we could have lived without but is being forced down our throats by an overzealous government agency. So instead of the simple, cheap two-way vent (a sealable hole) that used to be on portable tanks, now there's an expensive one way valve that only allows air into the tank, but will not release vapor out, (thereby causing the tank to become pressurized as the warmed fuel expands) and a fuel demand valve system. And of course, it ain't free. If anyone has noticed the outrageous price of portable plastic gas tanks lately it's because they all must use a special plastic now so that Ethanol doesn't effect them. Just another little cost/tax being forced on us by big brother. But I digress... the grey thing is as I described it previously, a safety device.

[Starzofchaos]

Have you thought about installing a Moeller Marine fuel tank? I am planning on replacing my old tank with one of these. Since the original is untreated aluminum, and for what ever reason that Wellcraft decided to foam the tank in causing the tank to corrode even faster.

Here are the links:

http://www.moellermarine.com/oem/fuel_tanks/fuel-tanks/

Do you have the measurements on yours? I have a 1990 Fish 18 and I was told it has a 50 gallon tank.

[mannydvk11]

Originally Posted by Starzofchaos

Have you thought about installing a Moeller Marine fuel tank? I am planning on replacing my old tank with one of these. Since the original is untreated aluminum, and for what ever reason that Wellcraft decided to foam the tank in causing the tank to corrode even faster.

Here are the links:

http://www.moellermarine.com/oem/fuel_tanks/fuel-tanks/

Do you have the measurements on yours? I have a 1990 Fish 18 and I was told it has a 50 gallon tank.

sorry i have not answer for some time but yes now am looking to see how to repair the problem i do use the regular outside tank for now works OK for now

i have taken out the boat a few time after fixing the reebs and rebuilding the carbs no problems yet by the way the t-top is holding strong i really like it. i add it a all around light you can see it on the pic

here are some pics