466 fuel vent hose 2001

[rfverdery]

It seems as if the fuel vent hose is leaking, but I can’t get over to it, is there any access in the salon to the vent hose or fuel fill hose on the starboard side. Filled up yesterday ran for about 5 hours and at the marina noticed fuel dripping from either the vent or fill hose. Took fill cap off and there was some pressure in the tank. Other than the pressure how else could fuel leak from a hose above the tank? Any advice would be appreciated. Thank you

[Midnightsun]

If there is pressure in the tank the vent must be plugged somehow. Collapsed or kinked hose or mud wasp nest in the line comes to mind.

It is common practice to put a loop in the vent line. Every time it spurts fuel upon fill up, the bottom of the loop replenishes with some gas. If the leak is in the loop bottom, then yes it will drip out. Most likely the case as todays ethanol fuels eat away at older non ethanol compatible rubber and since fuel sits in the loop it will occur there first. This is what a fuel vent loop looks like. https://www.sailnet.com/threads/why-is- ... 80&slide=0

Had this very problem on my previous 1997 boat however it was the fill line that got eaten away from the inside out. Should not happen but when you add a solvent that eats rubber to your line this will happen. Ethanol was a huge F up IMHO not to mention it must have caused billions of dollars in damage over the years wherever gasoline is used.

[Viper]

The loop should really be going UP from the vent, do a loop, then down to the tank. Looping it downward will result in other problems; like collecting water or fuel. Looping it upward will prevent liquids from remaining in the line which is what you want. The reason it's looped upward is so that any water that gets into the vent fitting will drain straight out again instead of going to the tank, it would also have to go uphill and through the loop before it can get to the tank which is unlikely if it's a proper installation.

Unfortunately I don't recall where the access points are to get to the vent fitting from inside.

[rfverdery]

Thank you for that info. The vent tube runs across the top of the tank then zip tied to the fill hose and goes upwards where I can’t see it as of yet. Maybe someone will remember how to access the tubes from the inside.

[bud37]

There really should not be pressure in the tank, when you get access make sure the line runs uphill all the way to the loop. Now that said if there is some leakage then one of the hoses has a crack or a joint has failed.......even if there is pressure there should not be a leak in a proper system.....have a real good look at where the leak is coming from.
This is a diesel, so it may just be a restricted vent and a loose fitting.....hopefully.

[Midnightsun]

Missed the diesel part, so forget the ethanol rant.

[Viper]

Are you sure it was a release of pressure when you removed the fill cap or was there a vacuum instead?

[rfverdery]

Now that I think about it I believe it was a vacuum. Does that mean something different?

[km1125]

Source of the post Now that I think about it I believe it was a vacuum. Does that mean something different?

Still means a plugged vent. Shouldn't have pressure or vacuum in the tank.

A plugged vent and a vacuum could actually collapse a tank. All depends on how good the fuel pump is and if it can still deliver fuel to the engine under that kind of a vacuum. On a gas engine with electric pumps the engine would probably starve first.

[Viper]

I asked because I thought it strange that there was "pressure" in the tank. Having said that, we shouldn't paint all fuel/tank systems with the same brush. While it wouldn't apply in this OP's particular application, we should expect depending on the OEM that some marine fuel storage systems after around 2010 can be more than just a tank, fill hose and deck fill, and vent hose and hull vent. Depending on the OEM, fuel storage on board is now a "system" intended to control evaporative/diurnal emissions (venting gas fumes to atmosphere), and overflow containment. In such a system, the tank isn't simply vented over the side at all times like we're used to. I'm pointing this out because in fact, in the design to limit venting, it's actually expected that the tank will pressurize due to external influences such as temperature. As such, a pressure relief system is incorporated in the design to release pressure at a certain spec but the tank can remain pressurized before this spec is reached. Most systems have their pressure relieve valves built into specially designed fill caps.

Ya check your venting system. If there was a vacuum, it's likely blocked. It's strange though that there would be a vacuum in a system that's leaking. You'd think with a leaking hose that pressures would eventually equalize through the hose at the leak even if the vent was blocked.