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Q1: what could cause a fuel tank to vent gasoline from the vent hose before the tank is actually full?

BACKSTORY
My 1999 OUTRAGE 17 [II] is in pristine condition. I am not the original owner. I believe the fuel tank was replaced by a previous owner. The fuel tank is made from a gray metal. The caulk on the deck has definitely been redone.

On the fuel tank a metal plate indicates the capacity: around 54-gallons, as best I remember. I have run out all the gasoline from the fuel tank, but then I was only able to add about 27-gallons before fuel started coming out of the vent.

When I thought the tank was empty the fuel tank level gauge indicated “E”, and when fuel began to come out of the vent the gauge indicated “F.”

biggerstaff wrote:Q1: what could cause a fuel tank to vent gasoline from the vent hose before the tank is actually full?

Q2: when you were adding gasoline to the internal fuel tank, was the boat on the water or on the trailer?

biggerstaff wrote:The fuel tank is made from a gray metal.

A below-deck permanent fuel tank on a Boston Whaler would typically be made from welded aluminum. The tank would typically have a metallized foil decal that gives the manufacturer’s name, the tank model, the tank capacity, and a date. This decal or sticker would typically be in full view when a deck access plate is removed.

The usual OEM would be Florida Marine Tanks. The typical capacity for a c.1995 OUTRAGE 17 would be 32- to 34-gallons. For a c.1996 or newer OUTRAGE 17 II the typical tank capacity would be 56-gallons.

Cf.: https://continuouswave.com/whaler/refer ... hulls11-19

This problem continues to baffle me. I've done a little more investigation. Below are the details.

• I was incorrect about the age of the tank. The fuel tank is original and was manufactured in September 1998. The model number is FMT-54A-BW and it holds 54 gallons. (That is slightly different than the 56 gallons that you find in the online specifications for my 1999 Outrage 17);
• when gasoline fuel comes out of vent (while on the trailer), the tank is indeed full. I inspected it, and the fuel tank level gauge agrees;
• I have run the fuel tank out of gasoline; the gauge says empty, but I, have not inspected it. [When refueling the fuel while on the trailer] about 27 gallons can be added before fuel comes out of the vent.

Give more more ideas. I am baffled.

When filling the fuel tank listen carefully at the vent fitting. As the tank approaches it's capacity the noise emitted at the vent fitting should become louder. At that point continue filling at a very slow rate.

Is there any reason to believe the fuel level gauge is accurate? Is the vent hose arranged with a loop above the fuel tank's top? When the boat is on it's trailer and hitched to the usual tow vehicle is the fuel tank level?

It could be interesting to run the boat until it is out of gas and carefully fill the tank to determine it's actual capacity.

Generally when adding fuel to the below-deck fuel tank on any Boston Whaler boat, the fuel fill inlet in the fuel tank is at the forward end of the fuel tank. If the fore-and-aft orientation of the boat during fueling is not with a down-by-the-stern trim, then the fuel being added to the fuel tank tends to accumulate in the forward end of the fuel tank. This tends to cause fuel to be expelled by the vent hose before the fuel tank level reaches full.

Depending on where the fuel filler hose enter the tank in the athwartship direction, the trim on the boat during fueling should be kept with the fuel filler hose side higher than the opposite side. This is also a good practice as it keeps fuel from being trapped in the horizontal part of the filler hose.

For example, on my boat the fuel fill is forward and the filler hose leads to the tank from the Port side of the hull. Accordingly, I usually sit in Starboard gunwale at the stern during fueling, giving the boat a list to Starboad and a trim down in the stern. This reduces the incidence of any fuel flowing up the vent hose during fueling.

Also, if the vent hose is part of the fuel fitting itself, there are often problems with that arrangement.

I recommend reading a long and detailed prior discussion that may be helpful. See

2019 Montauk 170: Adding Fuel a Problem
https://continuouswave.com/forum/viewtopic.php?t=4882

Also note when adding fuel with the boat on the trailer, the same preferences in the orientation of the hull need to be maintained. If the roadside gasoline station is on sloped terrain or if the orientation of the boat on the trailer puts a bow-down trim on the hull, you need to approach the pump from a direction that helps to overcome the bow-down orientation and (or) work on the trailer arrangement to get a better stern-down orientation for the boat.

A final remedy for the vent hose being part of the fuel filler fitting is to install a separate fuel vent fitting and move the vent hose to the new fitting.