can you help solve this gas tank vent problem?

sly_karma

sly_karma

Crew Member
When my bow gas tank is completely filled, I get some gas slopping out of the vent. I know I need to loop the vent hose as high up as possible but there's no room to go any further, it's right up underneath the bow deck. The picture attached is poor, it's a hard spot to photograph. Can anyone think of a way to prevent the gas slopping and water entry without lowering the tank? It would gain 6" but the storage space created is valuable. Is there some kind of check valve that could be applied here? I haven't come across something that would permit air movement but keep out water going same direction.

Yes, I know the hose clamp at the though-hull fitting is hanging loose at the moment...

2015-04-12 11.42.28.jpg
 
Look up fuel/air separators. I have a Racor model, but Attwood and others make cheaper ones. I got the Racor on Clearance, so was a lot less than normal. You have to watch when fueling as it cuts off the air vent and you can have the fuel bubble out the fill, if filling at a high rate.
 
I don't know if it will work on your boat but here is what I did on mine. I have my fill and vent on the side of my boat opposite my drivers seat. Water was getting into my gas tank from the overflow/breather vent on the side of the boat because the length of the breather hose was short and just went straight to the fuel tank connection. What I did was take a very long piece of breather hose, possibly 20' long and routed it down the side gunwhale looped it up higher in the side deck area and then ran it back to the connection on the gas tank. The length of the hose needs to be whatever it takes to do the re-routing. This way it acts like a plumbing trap. (But just to be clear here, it DOESN'T fill the hose with water like a plumbing trap would be filled with water). The hose does have some water in it and I can tell this because when I fill the tank the breather is exhausting air through it which forces out a few drops of water. Now if and when water gets in that overflow tube it just stays in hose. The added loop in the breather makes it even harder for the water to get to the tank. This has solved my problem of water getting in my gas tank which was actually a considerable problem. I used to change or drain my racor filter a few times each season. Now I only put a new filter on for each season. And I probably could get away without changing it. I just do it because it is good maintenance.
 
I change my fuel/water filter every season too, and I'm satisfied I'm getting negligible water in the tank. It occurs to me I could add a little more length and complexity to the line by adding a few 90 degree fittings near the tank so the surging is contained in a bit of a maze but the air can still flow in either direction.

I'd never heard of fuel/air separators before, will look into that too. Found this review of a few different ones for anyone else interested:
http://www.boatus.org/findings/40/
 
You could also change out your filler cap for one with an integral vent. Perco makes one that allows the tank to vent when filling, and is covered when the lid is closed, preventing water entering the fuel tank under normal conditions.
 
A loop on the flat... maybe. Sure dont want to create a P trap.
 
sly_karma said:
I change my fuel/water filter every season too, and I'm satisfied I'm getting negligible water in the tank. It occurs to me I could add a little more length and complexity to the line by adding a few 90 degree fittings near the tank so the surging is contained in a bit of a maze but the air can still flow in either direction.

I'd never heard of fuel/air separators before, will look into that too. Found this review of a few different ones for anyone else interested:
http://www.boatus.org/findings/40/
Click to expand...

Thats a good article/review. Thanks for sharing.
 
Thanks everyone for responses, several possibilities there. I'll try to do it without the separating filter first off as I have very little room to work with up under there.
 
I have noticed on my boat that if we fuel up fast at the end of fueling to absolute max. tank capacity that we can get a very little fuel spray from the air vent on the side of the boat. To stop it from happening we slow down the fueling rate with the nozzle when we think it is getting close to almost full and listen to the sound pitch going up indicating the tank is almost full and stop fueling just a tiny bit early as in don’t wait for the fuel auto stop to kick in on the fueling nozzle. At least with my boat, slowing down the fueling rate at the end and then don’t overfill results in no spray from the air vent. This may not work in your case but worth a try. Good luck with it as that is a frustrating problem.
 
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The new tank vent configuration had a sea trial today and it went well. As posted, I tried modifying the vent routing first because there is so little room for a filter up underneath the bow. The solution I tried was four PVC 90 degree barbed connectors used to create a square loop in the horizontal plane, as high above the tank as I could get. Fuel surging into the vent from a full tank has to make it past four abrupt direction changes to be able to vent outside. I didn't find any rough seas out on Okanagan Lake today, but nothing spilled out whilst on the water, driving to/from the lake, or filling the tank. Install was tedious due to tight spaces, but cost was a measly $10.
 
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