fuel tank problem

[Tellico Bob]

The main tank on my 1986 48 MY measures 220 gal. I can only fill it to just above 3/4. I have removed the sending unit and proved that it works and that there is space for another 60 gal. Checked the vent and it is clear. When fueling the nozzle shuts off at the 3/4 point. The fill goes from the deck turns 90 degrees towards the stern and then goes up to the ER ceiling and travels to mid ship before dropping straight down into the tank. Vent is next to the fill on the tank and is wire tied along with the ground wire until the fill turns up to the deck. The vent turns down and is attached to the thru hull vent fitting. when fueling the vent will spit a singe drop of fuel every minute or so. When I blew through the vent hose my helper said about a teaspoon of fuel came out. To my knowledge this tank has never been above the 3/4 mark and the vent goes straight up close to 4'. I am planning an 800 mile cruise in late Sept. and would like the comfort of those 60 some gal. The sending unit is at the aft end and the fill and vent are in the middle. The tank is 10' long.

 

[DavidM]

Your lost 60 gallons sounds like it is due to the fuel fill routing. I presume that it "goes up to the ER ceiling" to get over something on the way aft to the fuel tank. That "loop" is what is losing the 60 gallons.

So if you can't avoid going up can you cut a new fuel fill opening over the tank fuel fill inlet. Then run a short length of hose down to the tank inlet.

But if it were that easy the builder would have done it that way, right? Or maybe not.

David

 

[AusCan]

I agree with David's assessment.

You may have another option for filling up the tanks completely. Do you have any valves mounted on the bottom of the tank for equalization of fuel tanks? If so you could mount a small electric pump and fill one tank 100%, then fill the other 75% again. Then fill the rest from a jerrry can using the transfer pump again.

It would be a PITA, but for only one long range trip, it may be much easier/cheaper than re-doing your fuel filling system.

 

[Tellico Bob]

So why does the fuel nozzle shut down at the 3/4 mark? The nozzle as I understand it will stop the flow when pressure in the form of a liquid or air pressure is present and therefore the flow is stopped. There is no way that I can see liquid rising in the fill pipe since the tank is not full. The vent is clear and working as designed yet I found a small amount of fuel in the vent pipe. The vent hose is 1/2" ID and the fill pipe is 1.25". Is there some connection between the fill pipe and the vent being next to each other on the tank? I check the tank and it is pitched 1 degree foreword. That means when the nozzle shuts down there is still 2.5" of space at the aft end and there is less than 2.5" in the middle where the fill and vent are located. I have owned way to many boats over my 75 years and I have never had a boat that I could not fill the tank. Someone out there must have had the same problem and figured it out.
I have two 100 gal saddle tanks plus a 150 gal aux that I use for my generator. I burn between .9 and 1 gal per mile and I would like to know my range and 60 gal is 60 miles, HELP

 

[Rough Magic]

Is there a short tail on the fuel vent inside the tank? Say that magic 2.5 inches? I'd check that next.

Dave

 

[Tellico Bob]

Dave, I already started looking at that possibility on Friday. The vent fitting is about 2" high above the tank and I need to measure how far it extends into the tank. So if the vent extends into the tank and the fuel level reaches the bottom of the vent the nozzle will **** off? If this is the case I have a 185gal tank not a 220 gal tank. What are your thoughts as to the drip of fuel coming from the vent when fueling? I am going to take a piece of wire and bend a small 90 degree hook on the end and slide it down the inside of the vent tube. This should tell me how much of the tube extends inside the tank. My big problem right now is I am not going to be back to the boat until at lease 8/14. This has been a constant problem since I bought this boat having it three hours away. This is why I am planning a 840 mile cruise to bring it home and fuel capacity is important. Thanks for your input.

Bob

 

[Rough Magic]

The fuel is probably from topping off the tank. I'd guess the fuel fills the vent until the nozzle shut off is tripped. Also the vent should not have any low spots, loops, or kinks. Dave