Marlin Tank Really Full?

[hinmo]

I am confused with my new(er) Suzuki tank gauges. I thought I had about 70gal in my main tank and was filling up yesterday. At 10 gal pumped, it kept burping back at me like it was full. What gives? Could it really be full?

PS - I would prefer not to pull the sender and do a manual/visual if possible

 

[seasick]

I am not familiar with your gauges or their setup but I can warn you not to pull the sender if there is a chance that the tank is full. If you do, there is a good chance that fuel will flow out into the bilge.

A simple test to start figuring out what the story is would be to pull off the senders wire (pink I think) and use an ohmmeter to measure the resistance of the sender.Standard senders have a range of 33 to 230 ohms with 33 being the full position and 230 being the low/empty reading. So if you read 130 ohms your sender is at the half way point. Granted if the sender is bad, the reading will be misleading but assuming it worked before changing the gauges, I would think it still worker afterwards.

While you are at it, with the pink wire disconnected at the sender and making sure it is not touching any metal, turn on the gauge. It should read empty. Now touch that pink wire to a ground (the tank ground or the sender ground assuming the ground is OK. The gauge should read full

There also may be a configuration or switch setting on the new gauge for the sender type. Note that European senders read in the opposite direction where low resistance is empty and high is fuller.

There is also a possibility that a tank vent is blocked causing the gas nozzle to shut off but in that case, you can usually wait a few seconds and then be able to add more fuel till it trips again.
Let us know what you find out

 

[Legend]

I had that burping syndrome once on an old Mako. It turned out to be an issue with the fuel hoses to the tank. Over the years the skin material just soften up and was collapsing and blocking the flow of fuel. I eventually found it when I smelled gas fumes from bilge. are you having the same issue with your auxiliary tank?

 

[DennisG01]

The first thing I'd be looking into is that clogged fuel vent line as mentioned above. It could be that the hull fitting is clogged or it could even be that the vent line has developed a low spot and fuel is collecting there. I had that happen to me on a prior boat and one day when filling up (the boat was rocking around a lot from the wind at the dock) I experienced the same issues as you. It was a plastic, 50g tank and I could access by a full size removable hatch. When I opened the hatch to check things out, the tank was inflated like a balloon! I gingerly stepped on and realized I could step harder and harder. Eventually, a big POOF was heard as stepping on the tank forced the clogged fuel out. I fixed the low spot the next day and never had an issue again.

 

[seasick]

I suppose it would be helpful to know when the issue popped up. If it didn't trip the nozzle before the new(er) gauges but did afterwards, I would lean towards something with the gauge wiring or settings. In other words, the tank may indeed be full

 

[hinmo]

good points all. I will investigate more and report back if I find anything

 

[hinmo]

I just looked at the fuel fills, and there is a vent tube on the top of each on the inside. Oddly enough, I cannot see where they exit the hull (the vents). Do not see the normal thru hull vent exit. Anybody got any idea where they go?

 

[Ky Grady]

They vent inside the top of the fill, under the cap.

 

[hinmo]

They vent inside the top of the fill, under the cap.

oh - thats the vent output I am looking at. So there must be a connection on each tank...I didnt see it via the round access on the deck to the tanks...guess theres not much I can do to assure the vent is working tho

 

[seasick]

That vent line goes from the tank vent to the filler fitting which is combo fill/vent type. There are no external openings for venting on the hull. It is possible that the vent is blocked or restricted but that is not that common as compared to an external, separate vent fitting.
It is possible that you gassed up at a pump with a super sensitive nozzle but if that were the case, other boaters would have had the same issue. One way to test if the vent is blocked is to fill the tank till the nozzle triggers and then wait 30 seconds. Now try to add gas again. If the nozzle trips right away, the filler is full of liquid. If it pumps for a bit and then trips, there is probably either too much back pressure (venting issue) OR the filler hose has a partial blockage. In your case, since the tank took 10 gallons or so before the nozzle tripped, I tend to thing that now your tank is full.