Fuel Tank Vent Question

[SailorGoneBad]

I have a small, weeping leak before the shut-off on my port tank. I soak it up with a pad but it drives me nuts and it is time to fix it.

Step 1) Use up over half of my tank of fuel. (this is the best part but it talks a while.)

Step 2) Transfer the fuel from the leaking port side to the starboard side.

Step 3) Take everything apart, clean it, dope everything up and put it back together.

My question comes up at step 2. After a short while my transfer pump significantly de-pressurized the port tank. After I pried the the fill cap off there was an audible sucking sound of air rushing back in. And on the starboard side there was a noticeable but less pronounced burp.

I was not expecting this. I assumed the fuel tank vent would keep things equalized. Can the vent get blocked? Am I the last kid on the block to realize you need to clean these things? Or am I missing something obvious.

I have never noticed any problem while operating the boat but this old FL120 does not draw much fuel.

 

[rgano]

You have been limping along with a blocked port tank vent probably with fuel aligned to the FL from both tanks with the port allowing a little bit at the time to pass. Mud daubers are the most usual cause hereabouts for clogging vents, but a dip in the vent hose can end up being a problem. Some vents get kinked with time or even initial installation as a friend found out. If you have a vacuum which can be rigged to blow instead of suck put it over the vent on the side of the boat with the fill cap off and piece of paper over the filler opening. You should be able to blow the paper off. Even though it is diesel, I would not advise trying anything involving the suction of the sweeper/wet-n-dry vac.

 

[Giggitoni]

I don’t have an experienced answer to your question. However, I wonder if your transfer pump was moving the fuel too fast from the port tank and created a vacuum?

 

[SailorGoneBad]

Yup. Definitely blocked. The starboard side is not really any better. So what do you do? Stick a hanger wire in there? I would have to remove the water heater to get to the vent hose so I would really like to do this from outside the boat. I have visions of a pile of debris landing in the bottom of my tank. Is there normally a screen? I don't see one.

 

[fgarriso]

The only way to know you have it clean is replace the entire line with 1" fuel rated line.

 

[rgano]

I have seen with and without screens. A screen prevents the mud daubers from getting deeper into the hose and allows you to more easily see and remove their mess.

 

[O C Diver]

Most vents have a screen to keep stuff out. I would start with inspecting the screen and possibly cleaning it with an old tooth brush (most screens are accessible from the outside where the vent is mounted).

Ted

 

[Bacchus]

The only way to know you have it clean is replace the entire line with 1" fuel rated line.

I disagree! If the only way to know it's clean is replacement it becomes an annual replacement which is crazy. You may need to install an inspection plate or relocate the vent for easier access but I would modify it such that you could check & clean it easier by blowing or sucking hose and cleaning the ftg screen.

 

[fgarriso]

I disagree! If the only way to know it's clean is replacement it becomes an annual replacement which is crazy. You may need to install an inspection plate or relocate the vent for easier access but I would modify it such that you could check & clean it easier by blowing or sucking hose and cleaning the ftg screen.

Don,

Now stop and think about this. If his vent line is 6' long and fuel line cost 1/ft that would be $6 to know you have a clean vent line! No one said it was an annual replacement item.

 

[Bacchus]

Don,

Now stop and think about this. If his vent line is 6' long and fuel line cost 1/ft that would be $6 to know you have a clean vent line! No one said it was an annual replacement item.

How do you know its clean next year / season if replacement is the only way to know its clean?

 

[fgarriso]

How do you know its clean next year / season if replacement is the only way to know its clean?

WELL ............ I guess you could resort to sucking on the hose as you suggested.

OR...... Buy my $19.999999 fuel tank vent line cleaning kit that is guaranteed for one season or I will cheerfully return the unused portion of your money. patten pending and all that stuff

 

[SailorGoneBad]

surgical solution

The space between the port on the fuel tank and the fitting for the vent is cramped and I am not as nimble as I once was. I was thinking about removing the clam cover so I could get at opening better. Then replace it with something with a removable screen.

What are the rules for the location of the vent? Could I just put it in the cockpit?

View attachment 131470

 

[SailorGoneBad]

Solution... so easy.

No, I did not contort myself into the corner of my engine room at the back of the tank and replace the hose. I blew through the debris with an air compressor. I think they were spiders and their desiccated bodies are now drifting to the bottom of my tank.

43 years ago, some thoughtful Taiwanese guy installed a copper loop before the vent hose to prevent water from entering. This is great but it makes running a wire in to clean the vent very difficult. With the, I think largely decorative, clam shells cut off, cleaning is easy.

I'll need to clean it up and hopefully install a removable screen but, for now, I am back in business.

Thanks for the input.

 

[Bmarler]

Use extreme care any time you pressurize a fuel tank. You can easily damage the tank or blow a hose off. Fuel tanks are tested at very low pressures. Removing the fuel fill cap when blowing the vent clear is a must if blowing towards the tank.
Preferably, removing the vent hose at the tank and blowing outward would clear the line.

 

[SailorGoneBad]

Super good point Bmarler. Fill Caps removed before blowing out spiders. Your concern is what started this quest. I was surprised (and alarmed) when transferring fuel resulted in de-pressurizing one tank and pressurizing the other.

 

[hollywood8118]

Why push the stuff into the tank vs vacuum it out, again as many have said have the filler cap loose so as not to pull vacuum on the tank when the stuff comes out?
HOLLYWOOD

 

[SailorGoneBad]

I think pulling it out would be better but it would not come. Pushing it through was way better than getting at the hoses from inside boat. Muffler/ Exhaust pipe and hot water heater all in the way.

 

[Brooksie]

Why not try a vacuum pump, one with a tank would be better so you could build some volume. Think of it as compressed air coming from the tank. Don't forget to do it with the filler caps off.

 

[Mike GB32]

I had the same problem with the same vent hose and solved it in the same way. I found a replacement clamshell on Ebay and drilled and screwed it on instead of using adhesive. Now I can remove it to clear it again if necessary.

 

[Greg S]

How do you check to see if they are clear?

Every time you fuel up you should hear/ feel air coming out of the vent. If not, it’s plugged. The vents are almost always near the filling deck plate, but on the outside of the hull. To the OP, you don’t want them venting to the inside as they spew fuel if you over fill; from expansion; too much fuel return to one tank; or excessive foaming while filling. Another sign that they are open and venting while you fill is that you may get spitting from the vent from foaming or fluid collection in that loop you described.

The screen is there to be a flame arrester. A wire mesh screen will prevent flame from passing. Look up Davey Lamp or miner’s lamp. As a second feature, it helps keep bugs out of the vent tube.

 

[ronobrien]

You have been limping along with a blocked port tank vent probably with fuel aligned to the FL from both tanks with the port allowing a little bit at the time to pass. Mud daubers are the most usual cause hereabouts for clogging vents, but a dip in the vent hose can end up being a problem. Some vents get kinked with time or even initial installation as a friend found out. If you have a vacuum which can be rigged to blow instead of suck put it over the vent on the side of the boat with the fill cap off and piece of paper over the filler opening. You should be able to blow the paper off. Even though it is diesel, I would not advise trying anything involving the suction of the sweeper/wet-n-dry vac.

Agreed about the suction side of the vacuum, however I have used a method that works ON DIESEL ONLY NOT GASOLINE. I put the suction hose of the vac into the a hole bored in the lid of a 5 gal pail. Another hole is bored for a smaller flexible PVC hose. That hose is used to suck crap from the bottom of the tanks. The suction pulls stuff out, but it drops into the pail instead of the vacuum canister. A rigid section of PVC pipe/copper tubing can be used as a wand. I have used this to clean fuel tanks pretty easily and pretty effectively. A few turns of duct tape on the vac hose & tubing where it enters the pail lid prevent them from being sucked into the pail. It also help provide a seal so vacuum isn't lost.

 

[rgano]

Agreed about the suction side of the vacuum, however I have used a method that works ON DIESEL ONLY NOT GASOLINE. I put the suction hose of the vac into the a hole bored in the lid of a 5 gal pail. Another hole is bored for a smaller flexible PVC hose. That hose is used to suck crap from the bottom of the tanks. The suction pulls stuff out, but it drops into the pail instead of the vacuum canister. A rigid section of PVC pipe/copper tubing can be used as a wand. I have used this to clean fuel tanks pretty easily and pretty effectively. A few turns of duct tape on the vac hose & tubing where it enters the pail lid prevent them from being sucked into the pail. It also help provide a seal so vacuum isn't lost.

Very clever. I wish my current boat did not have the horrible S-shaped fill hose which makes it impossible to use such a wand. Also no inspection ports.