CONTINUOUSWAVE

Q1: what fuel tank level gauge and associated fuel tank level sender would be appropriate for a 2004 DAUNTLESS 16 to replace the OEM fuel tank gauge and fuel tank level sender that were Boston Whaler part 1746453?

BACKSTORY
I just purchased a 2004 DAUNTLESS 16 with a 2022 Tohatsu 115-HP engine. When I think the fuel tank level is at FULL, the fuel tank gauge reads just above HALF-FULL.

I have read [something somewhere] that although the fuel [at some location] overflowed at fill-up [unclear] does not mean [the fuel tank] is full.

Q2: could the cause [of the fuel overflowing at some location] be caused by [some other problem]?

Perhaps you are trying to say that when adding fuel to the 2004 DAUNTLESS 16 you get fuel splashing back at the fuel filler inlet fitting or you observe fuel splashing out at the fuel tank vent fitting. You then interpret this behavior as indicative of the fuel tank level being at FULL. Then when reading the fuel tank level from the remote electrical fuel gauge, the fuel gauge shows the tank level is HALF-FULL. If that is your intended meaning, then read on. If that was not your intended meaning, then ignore the advice below.

Certain models of Boston Whaler boats, including the DAUNTLESS, have a history of having a fuel tank inlet and fuel vent combined into one fitting. There are prior discussions about difficulties in adding fuel to the fuel tank with this arrangement.

For example, see:

Vacuum Lock in Fuel System in 2014 170 DAUNTLESS
https://continuouswave.com/forum/viewto ... f=6&t=8307

Regarding the fuel tank level gauge not showing a true reading of the fuel tank level, see

2003 160 DAUNTLESS Fuel Tank Level WEMA Sender
https://continuouswave.com/forum/viewto ... f=6&t=5631

ASIDE:
Your description of the problem you are encountering with the fuel tank on your 2004 DAUNTLESS 16 is difficult to understand. When describing a problem you should write more clearly and refrain from using the pronoun "it" to refer to components that have never been identified.

jimh--thanks for your reply. I will check out all your suggestions.

Twenty years ago the recommended Boston Whaler remedy to the problem was to install a separate fuel tank vent line running from the fuel tank to the hull port side and installation of a vent through hull fitting higher than the the top of the fuel tank. If you choose to do this remember to add a loop in the vent hose to prevent water from entering the fuel tank.

That modification was installed on our 1999 Dauntless 16 shortly after we bought it in 1999. It stopped the slow fuel filling problems.

Q3: can I simply fill the tank slowly to prevent the overflow?

My 2003 160 Dauntless had a separate fuel tank vent midships on the port hillside. The hose leading to the vent would occasionally get clogged, my assumption was that it was from splashing/sloshing fuel accumulating in a low point in the hose. Before refueling I'd blow into the vent to clear it. Yeah, that means I could be blowing some water back into the tank, but there was no practical way to suck the vent line clear. And that's what a water-separating fuel filter is for anyway.

In the following years the smaller Whalers were built with a vent line integrated into the filter port as Jefecinco described, but anecdotally this seemed like a "solution" that just caused more problems. I don't know when, or if, the 160 Dauntless got the new fuel vent.

Filling slowly will probably help, but the filler hose is likely to burp gas if the vent isn't clear. Filling the tank only part way may also help, and really, how often do you need 45 gallons of fuel on a 16 footer? I usually filled mine no more than 3/4.

Thanks - I too have a vent on the port side midship. I haven't attempted to "clean" it or see if its clogged, but will. This weekend I filled the tank slowly (needed 20 gallons) and a little "burping" at the top of the filler occurred, I let it settle, and put in more fuel. I am not overly worried about [the fuel tank level] as [the fuel tank level now is a] 7/8th-FULL--and that is the new "full" level--I am laughing aloud.