2019 Montauk 170: Adding Fuel a Problem

[Fossilhunter]

I have a 2019 Montauk 170 purchased in July 2019. Several times I've had problems with adding fuel. I've only refueled while on the water. I have used portable fuel cans as well as dock fueling pumps—but never while on a trailer. The problems are sporadic. I usually refuel while on the boat alone.

The problem seems to be from improper venting.

Just last week as an example. I started with a full tank. After burning a quarter tank I attempted to fill up at a dock—no luck. The fuel would not enter the tank without spilling over. I burned off another quater tank returning to my boat slip . I attempted to fill up with with a fuel can: same problem.

The next morning after my boat sat at the dock I was able to fill up with a fuel can no problem.

I guess that eventually the tank can vent on its own after a time. This is a problem as you can imagine while out on the water by not having the time to wait for venting to occur if it is blocked while docked at a pier to refule.

Having said all that I have been in touch with the Boston Whaler dealership. The mechanic—very helpful by the way—stated that in 2018 there was a problem with with the venting line bending or bowing causing the problem in some cases. I'm the first he has heard of with a 2019 model. So when I take it in to have it winterized and serviced they will see if that may be the cause and possibly shorten the line. Meanwhile they suggested I have someone standing in the bow while attempting to refuel due to the design and venting concern.

Q1: Has any other owner of a 170 MONTAUK had the same fueling problem?

Q2: If so, was the fueling problem corrected?

Q3: How was the fueling problem dealt with if not corrected?

— Mike

[Phil T]

This is not unheard of for several models. I don't recall the Montauk 170 II having it though.

Typically the culprit is the attitude of the boat is resulting in blocking the vent. I would take the advice and have weight placed in the bow.

Also take a look at the vent. It could be clogged or slightly blocked. If you can access the inside of the fitting, remove the hose from the vent fitting and run a snake through.

This diagram is from your owner's manual, as you can see if you have a relatively full tank and your bow is up, your vent (amidships) can be blocked.

fueltank.jpg (51.74 KiB) Viewed 12892 times

[Fossilhunter]

Thinks Phil. Your explanation Sounds right.

I'll see if I can gain access to the hose and vent. I'll post back and report on outcome.

Thanks—Mike

[Masbama]

I had a 1999 Dauntless 18 and it was horrible trying to fill the tank unless it was less than half full—-the same problem as described here. One would think that after twenty years Boston Whaler would get away from cheap fuel fill-vent combinations.

[Fossilhunter]

MASAMBA—I assume you sold the Dauntless. I would not blame you.

Q4: What tricks were you able to perform to attempt to fill the tank?

Q5: Did you place someone in the bow during refueling?

Q6: Did you let the fuel tank sit until it vents itself?

Q7: Were you in conversation with others who had the same problem?

Sorry to bring up bad memories but any info would be helpful to me and perhaps others who may be having the same problems. I cannot believe I am the only one.

I agree with your comment about coming up with another design on the fuel tank.

To spend $45,000 for a 17-foot with such a problem is a lot.

—Mike

[jimh]

Q8: If the tank vent is under the filler cap, and the filler cap is closed during operation of the engine, how is the vent kept open?

[Fossilhunter]

Good question about the vent cap. Several times but only now and then when I open the cap it gasps for breath for a couple seconds, most of the time nothing. Once it burped up a small amount of fuel and then cleared itself so I could refuel. Air pockets with some fuel in the vent line ?

[jimh]

My concern about the tank vent being sealed under the filler cap is for delivery of fuel to the engine. If there is no venting of the fuel tank when the filler cap is closed, then as fuel is withdrawn from the fuel tank by the flow of fuel to the engine, the air pressure in the fuel tank must start dropping. Most outboard engines have very strict limits about how much suction pressure can be tolerated in the fuel delivery hose. In order to evacuate 50-gallons of fuel from a completely air-tight non-vented fuel tank, the suction pressure would have to be greater than the negative pressure created in the fuel tank. The fuel lift pump on most outboard engines can tolerate only a few PSI of suction or negative pressure in the fuel delivery line. Having open-air vented fuel tanks lets the air pressure push the fuel toward the engine. A non-vented tank creates a suction back into the tank as fuel is withdrawn, making it harder for the engine to pull fuel from the tank.

That Boston Whaler has stopped using an open-air vent on the fuel tanks of their boats is probably not directly related to the cost, as has been suggested above in the comment that described Boston Whaler boats as having "cheap fuel fill-vent combinations." I would expect that the combination filler cap and vent is probably more expensive than a simpler filler cap and a separate vent. Also, I suspect there may be some gasoline vapor emission regulatory action by the Environmental Protection Agency that has influenced the design.

[jimh]

This diagram is from your owner's manual...

PHIL--thank you for finding the fuel tank pictorial drawing from Boston Whaler for the 170 MONTAUK and posting it in your reply. The diagram is very useful and quite surprising.

If I am properly inferring the orientation of the fuel tank in the boat hull, it appears that the fuel filler inlet is located at the aft end of the fuel tank. Is that the actual orientation?

[Phil T]

The tank diagram orientation is upper right is the stern, lower left is the bow.

The vent hose is the smaller one that connects to the middle of the tank.

Note item 11, the vent flap in the fitting.

The integrated vent is due in part to EPA regs as well as economics.

Every boat has some "isim's" (ref: Ferris Bueller) and you just need to learn its tricks.

[jimh]

PHIL--thanks for confirming the orientation of the fuel tank in the 170 MONTAUK puts the filler inlet at the aft end of the tank.

The static trim for a boat with an outboard engine on a transom is usually to be down-by-the-stern, due to the weight of the outboard engine being so far aft of the hull center.

If fuel is being added to a fuel tank on a boat that has a static trim down by the stern and the fuel tank filler inlet is at the aft end of the tank, the level of fuel in the aft end of the tank will be higher than the forward end. As the fuel level increases toward a full tank, there will be no flow of fuel into the tank at some point, and additional fuel will begin to back up in the filler tube.

Another influence on static boat trim during fueling might be someone standing in the stern of the boat holding the dispensing pump handle and hose (or a portable tank), and their weight (and the weight of the portable fuel tank they are holding) further adds to the boat's trim being down by the stern.

The best way to overcome this problem is to alter the static trim of the boat during fueling so that the boat sits on a perfectly level trim or sits slightly down-by-the bow.

The fuel tank system is quite complex, as it includes an upper level hose running from the aft end to the bow end of the tank. This is denoted in the drawing as callout number 3 and labeled "GRADE VALVE."

My inference for the function of the two devices called a GRADE VALVE is they permit fuel to flow via the external hose from one end of the fuel tank to the other end when the boat is on the trailer and the trailer is ascending or descending a highway grade or a boat launch ramp grade.

The grade valves and the hose connecting them permit fuel to move from one end of the tank to the other when the tank is partially full and the boat is inclined at some rather steep angle as might occur while on the trailer--or even underway if in really big seas.

The grade valves should also help during fueling by providing a path for fuel to flow into the forward part of the tank when the boat is trimmed down by the stern.

The vent location in the center of the tank will work best when the trim on the boat is precisely level, as any tilt to bow or stern will tend to cause fuel in the tank to cover the vent.

In comparison to the arrangement of filler and vent lines shown for the 170 MONTAUK, the classic OUTRAGE hull fuel tank has the filler inlet near the forward end of the tank, along with the vent inlet. The vent is to open air. The natural trim of the boat being down by the stern helps keep the forward end of the tank from filling with fuel before the aft end. The only instance I have encountered with adding fuel to the tank on my classic-era boat occurred at a highway filling station that was on the side of a hill. You have to orient the trailer so the boat bow is facing uphill in order to be able to add fuel.

(You might ask: where does one find highway fuel stations located on the side of a hill? This occurs often when the highway fuel station is located very close to lakes. Generally roads run downhill in the direction toward a lake.)

[jimh]

The integrated vent is due in part to EPA regs as well as economics.

The integral vent in the filler cap also has another influence: the elimination of a rather large diameter hole in the Unibond hull to accommodate the fuel vent fitting results in a improvement in the structure and rigidity of the hull.

Owners of older classic-era boats may be surprised to see how much of the Unibond hull is cut away on the inboard side of the external fuel vent fitting. This was done because the vent fitting was not long enough to pass through the entire thickness of the Unibond hull, and a relief is cut on the inboard side so the fitting can be fixed in place to just a small thickness of the original hull.

As I recall there was a problem with certain boats--the OUTRAGE 25 hull if I remember correctly--with the hull having insufficient stiffness and strength at the location of the filler and vent hoses. Boston Whaler was providing repairs to those hulls which had developed hull cracks in those areas.

On that basis the elimination of the open-air vent on the hull sides can be considered a modification that improves the hull strength and integrity. This is another contradiction of the assertion that Boston Whaler eliminated those vents to be "cheap."

[Masbama]

A4: Some of the tricks I used [to add fuel to the DAUNTLESS] were:

--waiting until the fuel tank [level fell to] at least half-full,
--unhooking the trailer and lowering the tongue, and
--reaching down and shaking the fuel tank vent tube while filling.

The fuel tank capacity was 60-gallons so I did not have to put in fuel all the time.

Part of the problem was the fuel tank and fuel fill cap were at the stern.

ASIDE ON ANOTHER BOAT:
Mike--other than the fuel fill problem, the Dauntless was a great boat. I did sell it and now have a 190 Nantucket. My 190 Nantucket has a screw-on cap midway on the port side, and I never have difficulty adding fuel.

[jimh]

Boat builders must comply with EPA rules about evaporative emission of gasoline as required in regulations. I believe 2012 was a epoch for the start of new and more strict limits on the release of gasoline vapor from boat fuel tanks. Accordingly, Boston Whaler boats made after that date are likely manufactured in compliance with the evaporative emission limits.

The EPA recognized that changes to the venting of fuel tanks from an open-air vent to a contained non-vented tank would produce new problems for adding fuel to the fuel tank. Apparently the methods and hardware that Boston Whaler has employed, while assumed to permit compliance with the evaporative emission limits, do not completely eliminate all problems in adding fuel to the tank. But as mentioned here, the problems are generally overcome by altering the trim on the boat during fueling.

As already noted in this discussion, adding fuel to a boat integral fuel tank has always been affected by the trim on the boat, and even with open-vent tanks there are situations where adding fuel can cause splash-backs or very reduced rate of fuel flow into the tank.

I don't think the general cause of problems in the 170 MONTAUK can be attributed entirely to the use of EPA compliant tank venting. Most of the problem seems to be due to the location of the fuel fill inlet at the aft end of the tank and the natural static trim of the boat to be down by the stern.