I always fill the fuel myself and have to go very slowly when at a fuel dock.

When I siphon fuel from a jerry jug into the tank, I use a 3/8 inch inside diameter hose and I never have a problem with the vent burping out fuel.

We have had this problem several times over the years. Spiders build a nest inside the transom fuel vent and keep the tank from venting. We remove the vent line from the fitting inside stern locker and clean the blockage out. Takes fuel at a normal rate after treatment.

Bill,

I had the same problem pumping fuel at the Jack London/Oakland fuel dock until an emplyee showed me a ball/gate valve on the side of the pump where the hose connects to the pump. I adjust the valve to below half way which solved my problem. Before I knew about this valve I'd have to hold onto the nozel handle and carefully monitor the flow. The valve is left in the "Full Open" position when the USCG comes in to fill their small cutters...

Chris

When I fill Caprice I use a slow speed and listen closely to the fuel going in. When it is about full I can hear a different sound, sort of like a gurgling sound, in the fuel tank inlet and I stop fuelling.

I don't remember at any time that a dockhand put the fuel in my boat They hand me the nozzel then turn the pump on. As a precaution when accepting the fuel nozzel I always ask, "This is diezel, right" ? It may sound unnecessary, but a C30 owner from our Club filled his tank with gasoline a few months ago.

Thanks much, Bill, for that nice write-up. Any time your air vent has a trap for liquid in it, you are quite correct that it would explain the burping when one tries to fill the tank too quickly. Let's hope that solved your problem.

When I fuel the tank, the vent line gurgles. That gurgle may be caused by the trap-effect in the vent line. The gurgling has always been an important cue for me, as I tell the assisting crewmember or gas monkey to listen for when the gurgling ceases. I stop pumping fuel when a) the gurgling stops, b) fuel exits the vent, or c) I hear it rise up the filler port...whichever occurs first.

My compliments, Bill, on your deductive processes and the excellent writeup.

I think the reason for the overflow is that the fuel tanks have baffles or are sectioned off so that the fuel does not move in the tank while underway - similar to waterbed design. So when you fill the tank fast the section that the fuel spills into fills up fast while other sections remain empty. The only answer is to filling slowly.

[QUOTE=chs1517;5263]Bill,

I had the same problem pumping fuel at the Jack London/Oakland fuel dock until an emplyee showed me a ball/gate valve on the side of the pump where the hose connects to the pump. I adjust the valve to below half way which solved my problem. Before I knew about this valve I'd have to hold onto the nozel handle and carefully monitor the flow. The valve is left in the "Full Open" position when the USCG comes in to fill their small cutters...

Chris[/QUOTE]

Chris, use pump #1, it has a smaller nozzle. It's the pump furthest west on the dock, towards Scott's. The other one has a huge nozzle for large powerboats.

I seldom fill up at a fuel dock as I use so little fuel I just bring a five gallon jerry can and top off every other time I go out. I have not investigated the fuel vent system on my boat but, it is almost impossible to fill up without spitting fuel out the vent either at the pump or via a jerry can. On my boat by the time I can hear fuel in the fill pipe I am already spitting some out the vent.

I do not beleive there is a check valve in the system and this surprises me.
Has anyone put one aboard their boat or know of one. I am talking about a small canister that has a float in it so when the fuel level gets high enough in the vent system the float rises and seals the vent so no fuel goes overboard.

Steve,

I think a vent needs to be able to vent at all times. Having a check valve to close off the vent would defeat the purpose, IMHO.

Duane,

The design of this type valve would only close the vent if fuel was present in the float chamber in the line. As you fill the tank, once the tank is full and fuel flows into the vent system the valve closes, fuel then backs up into the fill pipe where you can see it rather than it pissing out the vent at the transom unnoticed. Yes, the vent should always vent and would when the engine is running as the fuel level decreases it would create suction that would open the vent and allow air in. One area of concern would be if you topped off with cold fuel and did not motor for a while to bring the level down, the fuel could expand and cause problems due to pressure build up. If you motor breifly after fueling just drawing the level down a quart or so this should eliminate this issue. Also the float reservoir should be large enough to have an air gap at the top to compensate for the expansion of the fuel as air can be compressed the fuel can not. All late model cars have a system to prevent fuel running out the vent, they use an overflow canister that runs back to the engine and the fuel is drawn out of the canister after start.

I am just trying to be GREEN, and also I am tired of the fuel staining my transom below the vent.

Steve,

We agree that the current system is flawed in the fact that so many of us have to be VERY careful not to flow fuel out the vent, pollute the water, and stain the transom gelcoat.

You are correct that a special venting system could be contrived to make that flaw go away. I was thinking of the issues you raised and the fact that a simple check valve probably would not be the answer.

I am going to try to check my vent hose for traps as Bill Matley suggested.

There is a cheap device you can get to stick in the vent line:

[url]http://www.greenboatstuff.com/grmafuwh.html[/url]

There is also this:

[URL]http://www.greenboatstuff.com/fuspguspprsy.html[/URL]

[QUOTE=stu jackson c34;6056]Chris, use pump #1, it has a smaller nozzle. It's the pump furthest west on the dock, towards Scott's. The other one has a huge nozzle for large powerboats.[/QUOTE]

The pump I was reporting is pump #1...cs

I did the modifications to the fuel vent hose and the difference is amazing. I used a 1 1/4" hole saw to make the opening to reroute the hose and a rasp made quick work to open the aperture so the hose would slide in. I needed to support the vent hose up in the newly opened hole so I jammed an empty beer can between the vent hose and the filler hose. (I signed and dated the beer can for when some future owner discovers this fix.) Took on 15 gallons in about 90 seconds with no spills or burps.

Just wish I could solve the vent issue for filling the aft water tanks as easily.

Tom Smith
Molly Malone
1994 Wingkeel Std Rig
#1332

[QUOTE=William Matley;5287]Let me offer what I believe is an explanation as to why some of our boats are difficult to fuel unless it is done slowly.

I have included 3 photographs to help illustrate my “slow filling theory”.
First, the area of our boat I am referring to is in the aft berth, the top of the fuel tank at the extreme aft end of the tank. The first photograph shows the larger main fuel pipe with the double clamps and the smaller black vent hose connected to the top of the fuel tank.

I decided to remove the vent hose to see if it was blocked by spiders or whatever. After disconnecting the vent hose from the tank vent, I pulled it downward, I had planned to push a fish tape up the hose and see if I could snag any blockage. What happened when I pulled the hose was a big surprise. About a ½ a cup of fuel poured out and onto the aft berth.

The presence of fuel in the vent is the clue to why we must fuel our boats so slowly.

Picture number 2 shows the plastic bag I taped on the end of the vent hose to catch the dribble of fuel but more importantly, it shows the large hole in the aft bulkhead created to allow the fuel fill hose and vent hose passage to the fuel tank. If you look closely, you can see that the bulkhead hole is lower than the vent (just out of view on top of the tank). For fuel to have remained in the vent hose since last September, there has to be a dip in the hose forming a liquid trap. Just like the trap under your home sink, fuel sits in this dip in the vent hose keeping the fuel tank from venting when fuel is added to the tank. This is why the fuel fill hose burps and spits unless you add fuel slowly.

So what to do?? Simple just eliminate the dip in the hose that created the trap.

I used an electric drill to drill a series of small holes going in a line upward from the top of the round bulkhead passage hole. After I made 2 lines of small holes with my drill, I used a larger drill to expand the small holes and with a screwdriver and hammer, broke out a slot for the vent pipe. Photo number 3 shows the finished slot cut with the aid of my electric drill.
Now there is no dip in the vent hose and hopefully no longer any need to baby the fuel nozzle.

I haven’t tried out this new vent hose modification yet and probably won’t fill the fuel tank until July some time but I didn’t want to wait until summer to pass along this theory. Please look at your own situation and judge if this vent pipe dip is (or is not) the cause of your lazy fuel filling.

While I am confident that I have solved my boats fuel problem, I admit I have been confident about enough other things to remember I could still be wrong.[/QUOTE]

Thanks for this info. i must try it.
I do put a catch basin on my vent so as not to spill.Not sure where to buy them though. Also, make sure you don't have water in your propane locker vent hose as I did. The consequences could be worse!

Spilling fuel out the vent line is bad for everyone, there are at least three different devices you can install to prevent spills, one is a new deck fill that returns the fuel to tank, another is a whistle installed in vent, and my favorite a Racor air/ fuel seperator installed in line in the vent hose about $100 on Amazon or Defender https://www.defender.com/product.jsp?id=133911