Fuel vent "spewage"

[MV Wanderlust]

We have our boat, finally! It's a clean and very comfortable 1986 Chris Craft Catalina 426 with Cummins 6BT 330 hp diesels. We're three days into our repositioning trip and have noticed a situation. When refueling, if the flow from the pump is much beyond a trickle, fuel dribbles out of the small vent on the side of the hull. That's definitely not right. It doesn't happen when underway, only when refueling. We checked the small chrome vent caps. They have a screen over them so it's unlikely any mud daubers flew in there and nested. (We're told that's not uncommon in this area) Has anyone encountered this before? If so, how do we fix it? We can refuel... it just has to be done at a painstakingly slow rate.

[Dave852]

Most likely there is a trap in the vent line filled with fuel. I would place paper towels under and fill at top speed. After the small amount that's stuck in the trap is blown out you should only get vapor.


Sent from my iPhone using Cruisers Sailing Forum

[Fiveslide]

Take a look at the route of the hoses for the vent and the tank, see if something looks kinked, or not enough slope on the hose to the tank, check for an obstruction, or something. If nothing can be found you could put an upward loop in the vent line so that it goes above the deck fill, but you could over fill the tank easily that way.

Until you find the problem, put a bucket under the vent to catch the fuel. I do that every time cause my boat will spit a little bit out the vent when it gets full.

Sent from my XT1080 using Cruisers Sailing Forum mobile app

[Lepke]

Considering the oil sheen on water laws, it's a problem that needs fixing. By the time the CG gets a couple calls on your boat, it can get expensive.
The vent line needs a loop and exit far above the tank top. Mine are 6' above the tank tops. The best setup is vent into a tank with a float alarm.

[MV Wanderlust]

Well, we took a week to reposition to the west coast of Florida. Along the way, we discovered a couple of things. We hit some four foot seas... which causes the fuel to slosh around and stir up some serious algae that we didn't know was there. It clogged the primary and secondary fuel filters. Much worse on the starboard side, which completely shut down. We limped into port and found a mechanic who diagnosed the problem. We changed the primaries. He blew out the fuel lines and cleaned out the racors. Then it dawned upon us... the owner hadn't run the boat much in about four years. He also probably hadn't kept the tanks full. Per the mechanic, this is not an uncommon cause and effect.

We found some Biobor JF... highly recommended... and dumped it into all of the tanks at the "shock" strength level. Then, every time we stopped for the night, we refueled and added a dose of it at the "maintenance" strength. We think the algae had gotten up around the point where the fuel filler tube enters the tank and was restricting the speed at which fuel could be introduced. Filling it too fast caused fuel to escape through the vents. Since we began the Biobor treatment, we can now fuel at normal speed until it gets to the point where the tank is full and starts to backfeed up the filler tube, which will result in vent spewage. The problem seems to be getting better and we have much cleaner racors, too.

In the interest of full disclosure, I have no financial stake in Biobor. It seems to be helping our issue.

[a64pilot]

Biobor is good stuff, and if you haven't gone through at least a half dozen filters, you caught it early, pretty early which is good.
I always use Biobor at every fill up, and at least half the time I have the attendant tell me I don't have to use that stuff, their fuel comes with it already in it. I use it anyway.