Second fuel tank vent

Dear All,
When filling the gasoline fuel tank on my boat I'm often experiencing blow back lately, tank also takes ages to fill fully.
I understand all this might have to do with the tank vent not working properly.
The vent hose running from the tank to the opening in the hull is however impossible to reach (without major cutting work).

I'm considering leaving the current one alone, and just add second one.
What would be a nice solution?
Tank is XPE material, hull is GRP.

Big thanks,
V.

 

If it worked well before, it is likely there is a clog. Have you tried opening the fill and blowing air back through the vent? Also, bees, spiders, and wasps make nests inside the vent outlet.

 

Thanks, probably best to try that first.
Think I will use some thick nylon wire to remove any clog(s) in the vent hose.

 

The most common issue is mud dauber filled the end with mud.

If you don’t have access to the outlet well; you could try a piece of wire and quick bursts with a vacuum.

 

An electric vacuum cleaner has an open motor that creates sparks. Sucking gasoline fuels may cause an explosion.

 

Yeah, I understand, this is why I said a quick burst of suction. But I’m glad you point it out.

As a technical matter, the vent attachment to the tank is required to be accessible, so he should be able to remove the hose from the tank for all efforts.

 

Ensuring that the vent line is clear is certainly the first step as many contributors have pointed out.

Most fuel lines are 3/8" and most vent lines are 5/8", non permeable approved marine grade hose. You did not specify the HP.
If you have a standard fill fitting, normally 1 1/2 inch, for gasoline AND the filler is quite open (as compared to the newer low emission type) most of the displaced air will come out of the fuel
filler neck.
Back in the 7o's the majority of our fabrication business was building auxiliary fuel tanks for pickups as the OEM's did not provide them from the factory. (Some Chevy's had 16 gallon fuel tanks. It did not make much sense if you had a 454 ci, engine and pulling a heavy load) In a good year we built over 3000 tanks. The joke at the time was that the range of such a rig was to
the next gas station.

The very biggest issue with poor venting/poor filling was that the vent line had a bend in from the vent to the fuel tank. Ie a low spot where fuel from the tank could slosh into it and lay in the low spot, restricting flow.
In a boat, water ingress into through a poorly located vent fitting is very common.
Not sure where how your vent line is routed but it should come in through the side of the boat, loop up say 4 inches or more so that if you have water ingress it will drain out (coming from a poorly located vent) and then downward to the tank without any low bends.

Check to see if there is a low spot where fuel can trap in a lower bend.

There is a slim chance that there is a tight bend in the 1 1/2 inch filler hose right close to the filler neck and the fuel can splash back and trip the fuel filling handle.

A question: Does the tank fill slowly all the time or only when it it gets say 3/4 full?

 

Did that work?

 

Any luck clearing the line @Vronsky or did you end up twinning the vent?

OR

Did you simply give up?

 

Thanks all !
I got myself one of these endoscope camera's.
Next time I'm go to the boat I'll try to inspect that hose.

Mighty handy to view other hidden/hard to reach spaces aswell.

 

Filling goes fine.
When tank is full to the brim, and I put the cap back on, the level drops again significantly when taking off the cap later again. This repeats 4-5 times before the level does not drop anymore, and the tank appears to be 100% full, having added 15-20 liters in total.
No fuel comes out via the vent opening in the hull side.
Manufacturer of the tank -Roto in Slovenia- suspects it might be tank deformation.