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Go Back   SailNet Community > On Board > Gear & Maintenance > Huh? - fuel tank issue
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Thread: Huh? - fuel tank issue Reply to Thread
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Topic Review (Newest First)
06-24-2008 01:04 PM
chucklesR Nunzio,
Once you get this problem 'fixed' and know your tank is full, take dowel rod and stick it down into the filler vent until it hits bottom - it makes a pretty good accurate guage of when the tank is full. Keep track of engine hours and such and you can put additional marks on it to let you know how much fuel you really have.
I'm not mathmatically inclined, but other owners have Gemini's have calculated that one inch of fuel in either of our tanks (18 gallons each, 11.25 inches sq on the base) comes out to .625 gallons per inch on the dip stick - that's a whole lot more accurate than a needle waving from 1/4 to 1/2 tank.
06-24-2008 12:39 PM
sailingdog I would highly recommend moving the vent hose to the tank if you can. Where it is now is a PITA and not a great solution IMHO.
06-24-2008 11:41 AM
nunzio Thanks.

The vent hose appears to be tapped off the fill hose and when the fuel backs up because of the "dip" in the fill hose it vents the deisel.

I just have to fill very slowly or get the dip out of the fill hose
06-24-2008 12:13 AM
Pub911 Here's another crazy idea...if the vent hose has a belly in it that could hold some fuel, the pressure of filling the tank could cause the simultaneous symptoms you are experiencing. But this would only be for a brief moment until the 'belly' flushes its contents. You still need to do something to address this if it's true, because you'll spew deisel every time you fill up until the belly clears itself out.

This would be a recurring problem if the dip in the vent hose was low enough to 'refill' itself when you tack or get in a seaway.

Hope this helps.
06-24-2008 12:06 AM
Pub911 Just to add some confusion to the thread....why are there only 3 hoses? Doesn't the engine have a return hose back to the tank for the diesel overflow? If you're boat is equipped with a 'lift pump', meaning it's not feeding fuel to the engine via gravity, but rather, it's assisted by a low pressure electric pump plumbed in line between the tank and the engine (typically between the primary and secondary filters) ...well if it has one of those try this...When the key is on and the engine is not running...listen carefully to the tank....do you hear fuel dribling back into it? If you do, it's coming from a 4th hose to the tank.

Now this may have nothing to do with the problem on the surface, but it may suggest you need to take a much closer look at the plumbing to get a deeper understanding...in hopes of improving your diagnosis.

Good luck.
06-23-2008 07:43 PM
nunzio You both are correct. The fuel line dips a bit below the tank and then routes to the top. Apparently I just need to fill it VERY slowly as the fuel will just spew out the vent.
06-23-2008 06:39 PM
camaraderie My guess is a blocked vent line...either with an insect next (wasps seem to love them) or with fuel collecting in a low point in the vent line and blocking the air. Disconnect the vent line at the tank and try to blow it out...If that is it...trace the line to eliminate low loops and future problems. If the tank air can't escape as you are filling it creates surges backup the fill line and gives the impression that the tank is overflowing.
06-23-2008 03:24 PM
JohnRPollard
Quote:
Originally Posted by nunzio View Post
New boat and my first fill up. Good point about the fast fill although we were trying to fill slowly. Question: Where is the vent line connected. Is it the fill ine or the furl tank? I think my first note could be wrong that the thiord line on the tank id a "return" line and not the vent which means the vent line may be tapped off the fill line.
Usually the vent line is tapped right into or near the top of the tank, then leads from there up to a high point in the hull or side of the coachroof.

The return line is for excess fuel that the fuel injection system does not use, so it gets pumped back to the tank from the injectors. You should be able to trace that line fairly easily. There should also be a fourth line, for fuel delivery coming from the tank to the fuel filter/pump. It will look much like the return line.

Now that I know this boat is new to you, and assuming you weren't using a high-speed pump, my hunch is that you have a low-point in the fuel fill line. Go down to the tank and see if the fuel fill line dips down a bit below the fitting where it attaches to the tank. If so, that is the culprit and you can try to fix it or live with it by pumping slowly. Sometimes there's no way to route that fill line without it taking a little dip before it gets to the tank.
06-23-2008 03:23 PM
nunzio The tank is definitely not full. I'm going down there today to track the vent hose.

Thanks,
06-23-2008 03:05 PM
Rockter If the tank has an inspection hatch, loosen it a little and watch for fuel squirting past the seal. If it does not squirt past the seal, take it off and have a look inside. If it squirts past the seal, the tank is full right into the filler hose.

If it's not full, have a friend fill the tank from the filler line and have a wee look in to see if the fuel is entering the tank OK.

I fitted a quick-release inspection hatch to the tank top, and I fill from there, in the cabin. Personally, filling right to the deck fitting can give an old tank a hard time as it raises the average pressure in the tank by about 1.5 psi (4ft head diesel), and 1.5 psi over the top area of the tank... maybe 4 x 4 ft, that's (2304 square inch).... will be a fair old load on there, close to 1.5 tons, on the roof of the tank, and probably the floor too.

Very few boat owners would park a 1.5 ton automobile on the roof of the tank, but plenty of them use 1.5 tons to try to lift the roof off the tank, or blow the floor out of it. All they have to do is fill their 4x4 ft tank right to the deck filler entry, 4 ft above the tank top.

Not for me that one.


Rockter.
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