Not the usual gas tank venting problem

[Ristin]

Recently purchased a really clean & mechanically sound 1984 Seaswirl Sierra. She's my first boat and so much fun. Has the 3.8l OMC stern drive and she runs magnificently.
However...(there's always a however right?)
She has a 31 gallon fuel tank mounted under the floor just forward of the engine. The filler port and tank vent are mounted horizontally through the transom near the top. The two times I've filled the tank I get a blast of fuel spraying out of the vent just as the fuel nozzle clicks off.
The first time I filled the tank I stuck the nozzle in and went full bore. When gas sprayed out the vent it got on my pants and shoes, and ran down the transom getting on the bellows and silicon around it. Estimate it was a cup or two..
Next fill up I set the fuel nozzle at the first click and tried filling slower. As I heard the tank get full I reduced the flow rate as slow as I could. She still blew gas out the vent when the fuel nozzle clicked off. This time I was standing to the side ( maybe you can teach an old dog new tricks) but gas still ran down the transom and onto the ground.
After fill up she doesn't spray gas out during transit even on bumpy roads.
Any thoughts on what to check?
My shade tree mechanic side was thinking of taking the vent off and putting a thin plastic or metal piece between under the vent housing and fiberglass to deflect the spray away.
Fortunately the side of me that likes to fix things properly came to this site for advice.
Thanks

 

[roscoe]

Welcome to iboats.

Do you need all 31 gallons in the tank? Must it be full?

I would suggest not filling all the way.

Turn on the key, watch your fuel gauge, when it approaches where it is normally full - and spraying fuel, just stop.

I'm sure someone will be along and give you other ideas.

 

[tpenfield]

:welcome:

The issue is because you are actually 'filling up' the fuel tank. So some fuel is getting into the vent line and causing a 'wet burp' . Try keeping it a few gallons short.

The vent system in boats is different than in a car, because the vent line typically travels horizontally for some distance under the deck and can 'trap' some liquid. A car venting system tends to be more vertical and allows the vents fumes to 'percolate' when the tank is full.

There are also folks who fill their fuel tanks for winter storage and find that fuel comes up out of the vent due to the vapor pressure. Boat tanks tend to do best at 3/4 - 7/8 full.

 

[Grub54891]

When you hear the gurgling in the filler or vent, stop! It's full enough.

 

[Redfred1]

I had that problem on my boat just after I got it. The previous owner replaced the vent hose and it had akink in it. I just loosened the top clamp and readjusted the hose.

 

[roffey]

I have a relatively new boat, 3 years old and it does the same thing. As stated above I just slow down the fill rate when at the top part of my tank.

 

[Brandon5778]

My boat does the same exact thing, I just thought it was normal to boats. When I hear the gurgling sound I stop and don't get sprayed.

 

[shrew]

You should really only be filling the fuel tank 90-95%. I shoot for 90%. 95% would be fine if you plan on running the boat and burning some fuel immediately. You need to allow for expansion of the gas when it warms up. Fuel in storage tanks are typically cooler than fuel sitting in a boat tank where the boat is getting heated by the sun.

I'm actually surprised they didn't cover that in your safe boating course.

 

[Ristin]

Thanks everyone. Sounds like its normal and nothing to worry about. I'll back off on the total fill.

 

[Ristin]

You should really only be filling the fuel tank 90-95%. I shoot for 90%. 95% would be fine if you plan on running the boat and burning some fuel immediately. You need to allow for expansion of the gas when it warms up. Fuel in storage tanks are typically cooler than fuel sitting in a boat tank where the boat is getting heated by the sun.

I'm actually surprised they didn't cover that in your safe boating course.

Yeah...me to...um,er, yeah the safe boating course. (thinks to himself) dang I knew I forgot to go back to something

 

[Ristin]

Filled up again this time filling slowly and listening closely. Since there wasn't a diesel pickup idling next to me this time, (what is it with diesel pickup drivers & idling while fueling) I could hear the fuel start to gurgle so I stopped. No spray and I figure I was within a gallon or so of completely full.
I also noticed my boat sits bow high on the trailer even though the trailer is level on my truck. I pulled the fuel tank inspection cover off and saw the fill hose to the tank is forward of the vent line. With the stern low the vent hose will be fluid covered before the fill hose.

 

[Ristin]

.

I'm actually surprised they didn't cover that in your safe boating course.

Safety course now complete and yes, fueling was covered.