Clogged diesel tank vent

Hello all,
I suspect my port diesel tank vent is clogged. Does anyone have a suggestion for how to try freeing up the vent from the outside. Perhaps compressed air, a squirt of WD-40 or some other product that won't do any harm.
I figure I'd try the easy fixes first in case it's something like a spider nest or similar insect related blockage.
Thanks in advance.

Does it have a screen on it?

I would try some wire if it has a screen that's the problem if it doesn't have screen then you got bugs in it

No Capt.Bill11, it doesn't. It's a small knob with a gap on the bottom and a concentric knob within. Protruding about 1 1/2 " from the hull below the fuel filler.

I was thinking I might have an insect blockage of some sort. I was hoping I could squirt something in the vent from the outside to help break up the suspected " bug blockage" without doing any harm. Ideas? Past successes?
Thank you.

Have the same issue, fortunately access to the tank via a deck hatch which reveals a 5/8" brass end fitting for the purpose of measuring allows me to remove this during fueling allowing it to serve as a vent. There is enough of the actual vent to allow for tank breathing. This may be an out for you providing you have a similar measuring port.

Al-Ketchikan 27' Marben pocket cruiser

Thanks Al. No deck hatch. If I can't clear the suspected blockage the easy way I may have to try to re-do my vent lines. Hoping to avoid that if possible.

I've had success w/ wet dry vac sucking on diesel vent to free it up.
I resisted blowing as it would push whatever is blocking it into the tank

Interesting Bacchus! Certainly worth a try. Thank you.

SKS said:

No Capt.Bill11, it doesn't. It's a small knob with a gap on the bottom and a concentric knob within. Protruding about 1 1/2 " from the hull below the fuel filler.

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Some vents have a cap that unscrews. If yours fits this description, unscrew the cap and you should be able to figure out how to clear the vent. If you can match your so one in a store, read the directions on the one in the store.

You certainly don't have to replace the vent line just because the thru hull is clogged.

Why do you suspect the vent line is clogged?

Had the same issue recently. You could hear the air coming out of the fuel fill and then some fuel during refueling. No screens on my vents.
Got a piece of SS wire and was able to dig out a significant spider's nest.
No problem refueling after that. Keep the SS wire in my tool box for the next time.

Thanks guys. I'll try all of the above. I suspect it's blocked due to "burping" of fuel near top off and no "weepage" at vent. Also, the port side always takes less fuel so I figure a blocked vent is causing a slight vacuum as fuel is used making the fuel flow from the starboard tank easier by comparison.
Thoughts?

SKS said:

Thanks guys. I'll try all of the above. I suspect it's blocked due to "burping" of fuel near top off and no "weepage" at vent. Also, the port side always takes less fuel so I figure a blocked vent is causing a slight vacuum as fuel is used making the fuel flow from the starboard tank easier by comparison.
Thoughts?

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Shop vac keeps my tank vents clear. South Louisiana mud-dobbers fill every hole. lol

On Tango, my generator pulls from the Stbd tank, so I also always need more fuel on starboard.

I also have vacuum Gage's on both engines to monitor fuel filters and the benefit also tells me if a vent is blocked.

A tank burping can be caused by a long tank as it gets really full.

Air is trapped on one end for a while if the boat is not level.

Good stuff! Thank you guys.
I appreciate everyone's thoughts. I'm learning alot from this forum.

Bacchus said:

I've had success w/ wet dry vac sucking on diesel vent to free it up.
I resisted blowing as it would push whatever is blocking it into the tank

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I would be careful vacuuming a fuel line, since that might pass fuel vapor past the motor with sparks from the brushes... kaboom!

stubones99 said:

I would be careful vacuuming a fuel line, since that might pass fuel vapor past the motor with sparks from the brushes... kaboom!

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I don't think the threat is there with diesel fuel, but congratulaions on your 666th post!!! You devil you

Check and make sure your air vent line run from the tank to the vent is always Above or geographically higher than your fuel fill hose. The blockage you are experiencing could be a low hanging vent hose. It was on mine. After a deck full of fuel spill I discovered the problem.

Pgitug,
Thanks for the input. I'll look into that.

To clear one of mine, rather than suck on the outlet end using a shop vac, try sticking the shop vac hose into the fuel filler but hook it on the "Blower" side of the motor. That will blow out anything that's blocking the outlet.

One of my four tank vents was clogged, so it was useless to put more fuel in that tank. The boatyard said they removed a collection of bees clogging the line. Not aware of how they cleared it, but logic says they sucked or blew out the carcasses.

Pgitug said:

Check and make sure your air vent line run from the tank to the vent is always Above or geographically higher than your fuel fill hose. The blockage you are experiencing could be a low hanging vent hose. It was on mine. After a deck full of fuel spill I discovered the problem.

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I had the same issue!

Rob

I had a chronic burping fuel tank. Pursued clearing the vent by a number of means on the theory that mud daubers or spiders had created an obstruction. Then, with the replacement of that tank, discovered that the vent hose had come loose from the factory supports, resulting in low spot in the hose. When I replaced the hose, it was routed to establish a clear and regular gradient from the tank to the vent hull opening. Cured the problem. Worth a look.

Earlier I suggested that one might not want to vacuum a fuel tank with a vacuum cleaner to try to get the vent tube clear... I was told that no problem existed with a vacuum.

So, enter this in evidence:
Woman vacuuming gasoline sparks explosion at Titusville car wash

I understand that the thing being vacuumed is not likely to be diesel, but still something quite flammable.

So, don't vacuum combustible gases.

Stubones, the title of the thread is "Clogged DIESEL Tank Vent".
Yes, it would be disastrous to try this trick on a gas tank, but the conditions required to ignite diesel fumes just do not exist in a vacuum cleaner.
Even your diesel engine does not combust diesel fumes, but an atomized spray of liquid diesel.
Toss a lighted match into a diesel can, and it is extinguished in the liquid.

Passed along to me by a marine diesel expert....

"....., fuel injected into the cylinder of a diesel engine is atomized in order for it to evaporate faster, the vapor (what some call fumes) is what burns, not the atomized droplets. Droplets will not burn, they carbonize and that is what makes soot. "

Droplets or vapor or atomized mix or liquid, diesel still won't ignite in your shop vac, vacuum is just the opposite of compression, which is the other part of the equation.
If you're afraid to try and clear your diesel tank vent with your shop vac, by all means hire a professional to do it.
It would be a good idea to check the hose routing to the vent, as mentioned above. It should run uphill all the way from the tank to a point above the vent, then back down to it to avoid trapping.

Again...more input from the pros...

"" vacuum is just the opposite of compression, which is the other part of the equation"

I wonder what equation that is? Diesel fuel vapor does not need "compression" to ignite, it takes heat, like that provided by an electrical arc.

It is how an oil burning stove works...... Or an engine room fire....."

#2 diesel has a minimum flash point of 125.6°F. In open air conditions, shouldn't be a problem. However, and as many industrial tank cleaners have discovered the hard way, it's not that hard to hit 130°F in a hot environment in a confined space. Think south Florida in August, 85-90°F injection temp, and an engine room after a several hour pull. Might get you there.

As with all activities, the devil is in the details. Way too many people treat diesel like it's water.