Weird Fueling Behavior

Slowly but surely I'm getting my boat ready for the water later this spring but I've run into something which has stumped me.

When I bought the boat last Labor Day, I was told the tank was full. Later I had to have the transom replaced due to water coming all around my outdrive. Of course the engine and outdrive had to be removed, along with the fuel tank. After that repair, everything was replaced and the boat was winterized.

Later I noticed the fuel gauge said I just had about 1/8 of a tank. I asked the guy who pulled the engine for me what he had done with my fuel. "Nothing", he said. "The tank was light enough we didn't have to dump any." Hmmm....

The gauges were pretty flickery and some of them didn't work so I ended up getting my boat rewired and replaced the entire panel, adding on a Hobbs meter and an extra bilge pump (this one automatic). I mention all this because even with the new gauge, it didn't show much fuel. The only difference is now the gauges are rock steady.

So I take the boat to a gas station and fuel up. It took just a little less than 5 gallons before the vent started leaking a little bit of fuel and the fill nozzle started to pop off (as they do when the tank is full). It seemed odd but I'm still not putting 1 and 1 together. But when I get home I check with the fuel gauge again and it's only reading maybe 1/8th tank again.

I try poking a coat hanger down the fill opening on the transom and it comes back wet, though I'm certain I didn't get it very far in. I finally got around to measuring the size of the tank: 16.5"X17"X18"=5049 cubic inches= 21.85 US gallons.

I had thought that either the seller or the guy who repaired my transom helped themselves to my fuel or it had never been fueled up at all. Now I'm thinking the seller THOUGHT he filled it because what happened to me, happened to him earlier.

I disconnected the fuel vent and blew some compressed air through the line from the external drain and where it connects to the tank. I didn't find any obvious obstruction. The fill tubing is a larger diameter and it seems to be a little constricted where it ties in to the underside of the transom filling port. The constriction doesn't seem to be enough to cause this but I don't know what else to think. This is weird.

The tank, FWIW, is metal and appears to be in excellent condition. Anybody have any ideas?

Re: Weird Fueling Behavior

Can you get to the fuel sending unit on top (possibly under a hatch)? If so, disconnect the battery and remove the sender. You obviously have a problem that you need to diagnose anyway. Look into the tank and see how much fuel is in there. Then you can see if you have an obstruction in the fill hose (sounds like it might be collapsed on the inside...just a guess). Even if the vent were clogged, eventually the gas would go down the tube as it is displaced by air.

In either case, you need to verify just how much gas you actually have before you begin troubleshooting.

Re: Weird Fueling Behavior

You might try cleaning the connections at the fuel guage sending unit on the tank...rule out bad connections before you break the seal for the sending unit. Good luck bro !

Re: Weird Fueling Behavior

Ever since they added the vapor recovery system on the gas pumps I've had the same problem when i fill up at the stations. Just have to go slooooow. PITA The marina without the system was full go to top. Try the station again, but lookout for the blow back

Re: Weird Fueling Behavior

Does it have the same problem if it's sitting in the water while fueling?

What you describe is pretty common when the fill hose enters thru the top of the tank. The tanks with the fill on the transom end of the tanks are notorious for being hard to fuel on the water. Tanks with the fill on the bow end of the tank usually run into problems fueling on the trailer.

The reason, boats tend to sit ***** heavy in the water, and front heavy on a trailer. The fuel collects at the low end of the tank which partially blocks the fill hose. The fuel backs up into the fill hose kicking out the backflow preventer on the pump. Hose entry in rear of tank, have everyone stand on the bow. Hose in front, have everyone sit on the transom while fueling.

Re: Weird Fueling Behavior

Check the fuel fill hose and vent line to see if either or both have a sag in the hose where fuel can collect and cause it to not vent or fill properly while filling......

Re: Weird Fueling Behavior

My guess is the fuel tank vent line has a low spot in it. If she were mine....the first thing I would check is to verify the tank vent is traveling uphill all the way to the vent. Low spot=problems with fueling process.

Best wishes!

Re: Weird Fueling Behavior

Use your trailer jack and level the boat bow to stern. You might be surprised how much your gauge comes up, if its working.

Re: Weird Fueling Behavior

burp said:

Check the fuel fill hose and vent line to see if either or both have a sag in the hose where fuel can collect and cause it to not vent or fill properly while filling......

Click to expand...

The fuel fill line is very stiff and seems to have a slight crimp to it where it makes the bend up to the fill fitting on the underside of the transom. The fuel vent line is smaller diameter rubber hose and appears appropriate. The tank itself is practically a square aluminum box with all its fittings and the sending unit on its top. The boat is on a trailer and while I happen to have the boat tilted bow high for drainage now, it wasn't when I was at the gas station.

I do not believe the fuel gauge is reading low. I can easily wiggle the tank; something I doubt I could do if it were full. I can shake the boat and create a sloshing sound in the tank. I don't think there's all that much fuel in there.

I'm starting to lean towards a problem with the fuel filler hose.

Re: Weird Fueling Behavior

Take the sender out and see what's actually in there. Then while yu have the sender in your hand move the arm up and down and see if your gauge moves. Then you know if that works.

Then disconnect the vent hose and make sure it is clear and there are no low spots.
Then the same with the fill hose.

Shouldnt take that long to check the whole system out.

Re: Weird Fueling Behavior

Just a dumb question what does the gauge on the tank it's self say?
Does it also read 1/8 tank or does it say full. The tank gauge is normally under the tank inspection plate and is a mechanical gauge I believe required by the Coast Guard.

Vent line should come off the top of the tank and rise all the way to the vent port.
It should not have any low spots in it where fuel can block the air going to the vent.

Re: Weird Fueling Behavior

Boatist said:

The tank gauge is normally under the tank inspection plate and is a mechanical gauge I believe required by the Coast Guard.

Click to expand...

None of the three boats I've owned has had a secondary gauge anywhere. Is this a recent requirement?

I agree with LAC_STS. Pull the sender and see what's actually in the tank.

My .02

Re: Weird Fueling Behavior

I'm voting with the leveling opinions.

Re: Weird Fueling Behavior

Does NC require the vapor collector at the fill nozzle? If so, pull it back to bypass it during filling. If no problems occur your tanks vent is the culprit. The internal vent tube goes all the way to the other end of the tank, above the anti surge/slosh plates. It may have gotten too low somehow.

Re: Weird Fueling Behavior

Do yourself a favor. Pull the "arm type" fuel sendor out and throw it as far as you can. Replace it with reed switch sending unit. No more fuel gauge bouncing all over the place.

http://www.iboats.com/Moeller-Reed-...0136488--**********.796699148--view_id.368241

Re: Weird Fueling Behavior

Update: after all the screwing around with the plumbing, it comes down to the main fuel line from the filling port to the tank is crimped.

As for the fuel tank itself, it turns out the fuel level sending unit was bad. New parts have corrected both problems.

Now the tank fills easily and the fuel gauge reads full. Life is good.

Re: Weird Fueling Behavior

Those fill hoses are a bear to install without dismantling the boat, thats probably why its got a crimp.

And on vent hoses, surveyors say they should have a riser loop .

"The Tank Vent

Improperly located fuel tank vent fittings are one of the top causes of water getting into tanks. When this is the cause, if you are a salt water boater, then it will be salt water in your tank. A fuel tank vent fitting on the side of the hull should be angled down and aftward. If angled in any other direction, you've got a problem that needs fixing. Watch out for deteriorated plastic and zinc alloy fittings; some of these things deteriorate incredibly fast.

The vent line should have a riser loop on the inside. That is, it travels upward first, then downward. If not, that is another potential problem."

Re: Weird Fueling Behavior

My first boat had an outside vent, the vent hose on it rose up and had a loop that went above the vent opening then to the vent. I can say that I have had water come out of the vent before gas would. Without the loop I would have had saltwater in the tank. Current boat has vent to the fill tube at the top so no loop in it.

Re: Weird Fueling Behavior

I replaced my fuel fill line on my old '87 Chaparral recently and it was a bear. Had to cut a couple access holes and remove a lot of foam to get the old one out. It was a nightmare job. Used some round plastic access hole covers to cover the two holes I cut when I was done. Looks good now.

My fuel fill line was original to the boat and was leaking.

Good luck and get ready for some serious work and scraped knuckles!

Re: Weird Fueling Behavior

When I replaced mine, I just cut the old one out. The new one had enough flex to do the job. Good luck on yours.