2018 170 MONTAUK II: Fuel Odor and Excess Pressure in Tank

[Rylando]

I am noticing a smell of gasoline fuel in the sump area of my 2018 170 MONTAUK more than what should be normal.

I also noticed that in the heat of the day, when I lift up the fuel cap of the built-in 25-gallon fuel tank , the tank off gasses with audible hissing sound.

Q1: what is the cause of the odor and apparently pressure build up in the fuel tank?

My inference is the fuel tank is supposed to passively vent via the fuel cap as temperature changes, and that somehow this is not happening. The lack of passive venting is causing vapor to build and seep out in the sump area via [a leak in] the vent hose; the excess vapor in the fuel tank only relieved when I open the fuel fill cap.

Fig. 1. Rubber hoses perhaps part of fuel system.

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I also infer the fuel fill vent hose is clogged. The engine runs fine and does not stall and fuel goes in with no problem. The pry-up deck plates limit visual access. My next step is to pry up the deck plates to get access to all the vent hose.

[Moderator's note: deleted two badly framed photographs of the boat that mostly showed sky, houses, pavement, and fences, as there was no particular element of the fuel venting problem illustrated in th0se views.]

[Rylando]

Fig. 2. A photograph of a drawing of fuel system.

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Fig. 3. Fuel cap open position.

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Fig. 4. Fuel tank top.

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[Phil T]

Replace the thru-cap-vent-fill fitting.

Some owners have replaced the combined vent-fill fitting with separate fill and vent fittings.

PERKO makes decent fittings.

[jimh]

Q1: what is the cause of the odor and apparently pressure build up in the fuel tank?

The fuel tank is not properly venting; the vent mechanism may not be working as intended.

Check the tightness of all the worm-gear hose clamps seen in Figure 1.

Q2: are those worm-gear hose clamps part of the OEM installation?

As the boat is still quite new, contact the dealer for advice and possible remedy at no cost under warranty.

Q3: why is there (what looks like) sand laying on the top of the fuel tank and and the fuel limit valve as seen in Figure 4?

[Rylando]

Thanks for the reply.

Check the tightness of all the worm-gear hose clamps seen in Figure 1.

I will go through all the hose clamps, and, in fact, I have found one that was broken already.

As the boat is still quite new, contact the dealer for advice and possible remedy at no cost under warranty.

I spoke with dealer and they said essentially the same [as the comments made above]. Also, they they said they would pressure test the fuel system, and check all fittings.

Q2: are those worm-gear hose clamps part of the OEM installation?

As far as I know the hose clamps and everything is OEM.

Q3: why is there (what looks like) sand laying on the top of the fuel tank and and the fuel limit valve as seen in Figure 4?

Good question about the sand. I don't know [its source]. The sand is somewhat stuck in place.

I had to re-caulk the deck seam surrounding the helm seat as there was a cut in the caulking all the way around, as if someone had used a knife; it was causing water to leak into the sump space below the deck. I asked previous owner if deck had ever been removed, and he said no.

Also, the gel coat of the keel of the boat in being repaired.

[Rylando]

Replace the thru-cap-vent-fill fitting.

Some owners have replaced the combined vent-fill fitting with separate fill and vent fittings.

PERKO makes decent fittings.

Great idea, thank you

[jimh]

I had to re-caulk the deck seam surrounding the helm seat as there was a cut in the caulking all the way around, as if someone had used a knife; it was causing water to leak into the sump space below the deck. I asked previous owner if deck had ever been removed, and he said no.

Also, the gel coat of the keel of the boat in being repaired.

I don't think either of those defects would affect the fuel system, the odor of gasoline, or the excess pressure in the fuel tank.

[jimh]

[The dealer] they said they would pressure test the fuel system....

It seems already quit apparent that the fuel system is able to hold significant pressure, as you report that when the fuel filler cap is removed there is a noticeable escape of pressure. I don't see what value would occur if the fuel system were pressure tested, other than to find out that there is a pressure build up that is not being properly released.

I would ask Boston Whaler what amount of fuel tank pressure is supposed to be tolerated by the fuel system so that it complies with the regulations of the some agency of the United States government that has decided that all boat fuel tanks must be prevented from venting to the atmosphere unless a certain level of pressure occurs, and at what PSI should the fuel tank release its pressure to the atmosphere if its design is conforming to these regulations. Unless you know those specification, testing the fuel tank by creating an internal pressure sounds rather useless.

Boston Whaler as a boat manufacturer must deliver the boat for sale with a fuel tank that is not directly vented to the atmosphere in order to comply with federal regulations, but unless there is some specific CRIMINAL law in the United States that says it is a federal crime to alter the fuel system so it actually does vent to the atmosphere (as all boats have been doing ever since gasoline fuel was used in marine engine propulsion), you should be able to alter the fuel system to just vent to the atmosphere (like a million other boats).

When you empower bureaucrats to reduce emissions into the atmosphere, they find more and more meaningless and marginal instances where some molecules of hydro-carbons can be prevented from escaping as a vapor.

[fno]

I tend to agree with JimH on this subject. I suspect your vented gas cap only vents into the tank (and not out) as prescribed by the various and numerous idiots in Washington DC. The gas cap came from a vendor and that vendor has the specs. There you will most likely find that the vent is a one way. If not, then bugs have plugged your vent line and they can be blamed if you can find them. I would suggest a new fill cap that is somewhat older and more reliable or separate the vent line and add that to your boat. It's only the first hole you drill in your Boston Whaler that hurts the most...