I have an internal fuel tank on my aluminum boat and recently I think im having some issues with it. Every time I go out I fill up my boat full (or at least I think it is). The last couple times I have went out I can only get four gallons in a 20 gallon tank. And also I can only run the gas in very slowly (I cant even click the latch at the gas pump, it takes about 5 mins for 4 gallons). Also about the same time this started happening my fuel gauge wont register that the fuel tank is full and says the boat is completely empty, although it runs fine and I cant get anymore fuel in. The vent on the tank seems to work OK but just not 100% sure that it is working perfectly. Any idea what may be causing the gauge to read empty and why I can only get four gallons in at a time? Maybe its nothing at all and I am just being paranoid? Sorry if this question is clear as mud, but thanks in advance

Hey there and welcome to the forum.

Disclaimer: I am not a gas tank expert... nor have I ever claimed to be.

I would be curious if there is some type of screen in the filler neck or line to the tank. I have heard of cars that do have this screen get clogged (many times with a piece of foil that came loose when they poured in an additive) It will allow you to get gas in there but it will not let you click the holder on the pump. It will flow so slow it will shut the pump off. There may have never been a screen of this type in any boat for all I know but I would see if that is the case. I think I would try to run a bulb type siphon down into the tank and feel for obstructions. If you meet one you may have to find out if it is a screen and just how clean it is. If you can get all the way to the fuel without feeling anything that may not be it at all.

As far as indicated fuel amount. Does the fuel tank ever read full on the guage? Is it a float type sender? If it only has range of motion from empty to 1/4 full that is all the guage will read. I would be curious just how empty it really is and if I was testing it...... I would take another 1-2 gallon container of fuel out and just run the thing dry and see how many gallons would really fit. Maybe there are 16 gallons in there all the time and your guage sender is just reading it wrong. Have you been out on the water long enough to burn up 20 gallons of gas?

I think your picture is painted pretty clearly and I hope I was some kind of help to you. There are a lot of people around here who have probably forgotten more about boats than I will ever know.

Good luck to you. Post up when you are making some progress. I am curious what the problem is.

Scott

I would suspect that at least some of your problem is RVP, which stands for Reid Vapor Pressure. It is a measure of the volatility of gasoline. In winter months, oil companies blend gas with higher RVP so that it burns well at low temps when the engine is cold. Typically, they adjust their blend as the year goes on to lower the RVP and reduce the volatility for obvious safety reasons. As temps increase in spring and summer, the vapor pressure will create a bubble in the filler neck of your tank that can block fuel from entering. Since we have had a very rapid warmup this spring in the south, the oil companies haven't reduced the RVP of their fuels quickly enough. It's a careful balance that is as much forecasting as science, and sometimes they can't change quickly enough.

Well I finally got some time to go out and look at it. I took off the access hatch and shook the boat and could see/feel fuel in it, seemed to be full. Got me thinking the the gauge is broken. Anyone know how to tell what type it is, ie how it mounts within the tank to show fuel level, and how hard it would be to replace?

easy to replace if you can get to the tank to do it. academy sells a replacement, just read the directions carefully and do as instructed. they are all the same and this universal one will work.

I just had that problem with my Ranger that has been sitting idle for 8 to 10 years. The air vent was clogged.

Thanks for the ideas, I think I need to take a closer look at the vent for sure. Looked around on the internet for a couple hours the other night and that is basically what the consensus was. Ill keep you posted when I find out what it was for sure. Im probably gonna work on it tomorrow some time. Will let you know afterwards.

Also check for a collapsed or kinked filler hose.

Well opened my access hatch up, and found that the lines for both the vent and gas fill line are very thick lines with a fairly large ID. Traced back to the tank and dont seem to be kinked anywhere. The tank seems to be full, and just found out that it has a 40 gallon tank in it rather than the 20 that I thought it had! The level gauge for the tank still isnt working, I located the sending unit, but it is located a lot farther forward that what you could actually get at through the access hatch. Im thinking that to get this fixed is gonna be a lot more than what I can take on myself. Dont think I have the patience and know how to take the sending unit out to replace it. Anyone know how much this is gonna run me to get fixed??