Gasoline under floor: 2019 170

[bighead1970]

In mid-July 2023 I noticed the odor of gasoline emitting from under the deck of my 2019 170.

[The boat is of unknown model; perhaps it is a 170 MONTAUK. When mentioning a specific boat, please give the model year, the model name, and the length identifier so that readers can learn exactly what boat is to be discussed--Moderator].

In the stern at a drain plug about [one ounce] of gasoline had accumulated. The appearance of gasoline near the stern drain occurs every time I use the boat. [See below about type of use for this boat.]

I looked under the hatches for active gasoline, but I saw none. In the hoses that I can see or feel there are no gasoline leaks. There is no gasoline on the top of the fuel tank--that I can see.

Q1: should I pull the floor?

Q2: what could be [the source of the gasoline leak]?

Q3: [is the source of the gasoline leak] a crack?

Q4: [is the source of the gasoline leak] something I cannot see?

Please give me suggestions [on where to look for the source of the gasoline leak].


BACKSTORY

I bought [the boat identified only as a 2019 170 but perhaps is a 2019 170 MONTAUK] as a new boat in January, 2020.

The engine is a Mercury 115-HP and it has 700-hours of running time.

I use the boat to take long strips [offshore] to angle for Bluefin Tuna. The last trip was 60-miles out, for a total of 164-miles dock-to-dock. The boat [identified only as a 2019 170 but perhaps is a 170 MONTAUK] takes a beating [on these offshore trips] but [these offshore trips are] not abusive.

[frontier]

Check with your selling Boston Whaler dealer about warranty. [Repair of the fuel leak] may be covered under the ten-year-hull warranty or the three-year component warranty. Even though the boat is now slightly past 3 years from sale, that may be close enough [to get warranty coverage].

[The fuel system] hould not have failed so soon.

[jimh]

I am not clear on what boat you are talking about.

Q5: is the boat under discussion here a 2019 170 MONTAUK?

If you can confirm, I will edit the mentions of the boat to fully describe it.

For now, I am guessing you must be talking about a 2019 170 MONTAUK, sometimes called the 170 MONTAUK II. I am basing that on the mention in your narrative of a fuel tank that is below the "floor". The new 170 MONTAUK introduced in 2018 has a below-deck 25-gallon fuel tank. I also figured that if you had a range of 160-miles, you would need to have substantial fuel capacity.

ASIDE on OPTIMUM RANGE
To go 164 statute miles on a 25-gallon fuel tank suggests you need to get a fuel economy of about 6.56-MPG. If you are using nautical miles, then to get 164-nautical miles on 25-gallons you need 6.56-NMPG.

According to Boston Whaler, a 170 MONTAUK II with a Mercury 115-HP Command Thrust engine has a peak fuel economy of 6.79-MPG or 5.90-NMPG at 23-MPH or 20.1-NMPH. And those boat speeds are where the best fuel economy occurs for at any boat speed.

You must be measuring in statute miles. You don't have enough fuel to go 164-nautical miles: 27.8-gallons need.

But even with a 164-statue miles, your must be using about every drop of fuel in the tank, as 164-statute-miles at 6.79-MPG suggests a fuel burn of 24.15-gallons. When you got back to the dock you must have been consuming fuel in the supply hose, the filters, and in the fuel distribution manifold in the engine.

You will have to pardon me for this intrusion into the repair discussion, but whenever I see numbers being used, I like to look into the numbers to see if they make sense.My conclusion here: you must either be taking additional fuel with you on these 164-miles trips into the open ocean, or you like to live on the edge of disaster.

[jimh]

Q1: should I pull the floor?

Typically a Unibond hull Boston Whaler boat will have a fuel tank cavity molded into the actual deck structure, and another molded and removable deck section will be covering the top of the fuel tank cavity and the fuel tank. Often there are circular, removable, pry-out access plates in the removable deck area that reveal the fuel tank at the fuel filling inlet and at the fuel pick-up outlet and at the fuel tank level sender.

Removing the engine cockpit fuel tank cover deck will be quite a project.

Also, because your boat is covered by a 10-year-warranty, I suggest you do not remove it, but instead let an authorized Boston Whaler dealer inspect the boat, and if needed, the dealer can remove and replace the fuel tank deck cover section; that should keep the warranty in force. If you pull off that big deck section, the warranty might be considered voided.

I looked under the hatches for active gasoline, but I saw none.

If the 2019 170 has circular, removable, pry-out access plates--perhaps what you are calling "hatches"--you should remove them and inspect whatever can be seen through those access ports.

I do not understand the description of the gasoline fuel as being "active."

Q6: what is "active gasoline"?

[jimh]

Q7: regarding the appearance of fuel "at the drain", exactly what drain are you referring to?

Typically a Boston Whaler boat will have several drains. The engine splash well will have one or more drains. There is always a sump area molded into the cockpit deck in the stern, and there is a drain in the sump.

If you can identify what drain you see gasoline fuel accumulating in, readers will be able to offer you better advice on where to look for the source of the gasoline.

[jimh]

Regarding warranty coverage, generally the warranty will only provide a remedy for defects that were in the boat when it was manufactured and delivered. If banging around in a 17-footer at 60-miles offshore in the ocean jarred something loose, that is not an original defect in manufacturing.

[Phil T]

Inspect the fuel supply hose, the vent hose, and the fuel fill hose where they attach to the tank. Tighten the connections. If they used a crimped fitting, remove it and replace them all with a stainless hose clamps.

Check the in-line fuel primer bulb.

Inspect the fuel tank check valve or demand valve, if so equipped. Personally I would remove it if installed.

Open the inspection port and rinse out the fuel tank cavity. Open the fuel tank cavity drain and capture the outflow in a bucket. Observe the outflow. The fuel could be from a past event, and it had not been fully flushed out of the cavity.

Water test the boat again.

ASIDE: Do not expect Boston Whaler and your dealer to be helpful. Those days are gone.