How do I run out of gas before the tank is empty?

[AshleysRevenge]

Hello and thank you all for your past help.

I have an 85 gallon tank. Saturday we put 20g in the tank. At this point I am fully aware that the gauges are not accurate. That being said, while the boat was on the trailer when we put 20g in the tank the gauge went from a half tank to three quarters of a tank. Which would make sense if the gauge worked.

The last time we took the boat out (last season) we ran out of gas (so we thought) if we waited about 15min we could start the boat and run for about 30s. We did this along with drifting until we made it back to the ramp. Came on here and explaned our issue and was suggested to change all the fuel lines and filters. We did all that and still would not run for more than 30s. Got frustrated and gave up on the whole thing for a few months. Mind you the gauge was at a half tank this whole time. Some time in December I got the bright idea to put 10g of gas in the thing. Guess what the boat ran fine. This leads back to adding 20g last Saturday and going out on the water.

After running for about 1h15m the boat started to show signs of running out of gas. Fine. We immediately made a bee line for the nearest gas pump and barley made it. At this point we made the decision to completely fill the the tank up to ensure we would make it back. When we "Filled" the tank up (in the water) the pump kicked off at 35g. So if I was really empty wheres the other 50g? I was told while at the pump by a older fellow that this kind of boat would burn that much gas for the distance we had come. I guess my question after all this rabble, is there some kind of pick up in the tank that after time could have rotted off to a level where I can't access that other 50g.

It was suggested there might be water in the tank but I don't think the motor would be running very well on water?

At this point I seem to have a 35g tank. Also I don't know why there are 2 fuel lines coming out of the tank.

I'll post some pictures later of what I am looking at.

Thank you all in advance for your advice.

David

 

[agallant80]

Re: How do I run out of gas before the tank is empty?

Most gas tanks can't use all of the gas in them. For example I have a 80 gallon tank and I think the usable is like 70 (need the other 10 to slosh around I guess)

In your case I would start looking. Something is not correct if you have 50 gallons in the tank and the boat start running out of gas. I would start with the lines from the motor back to the tank and pull the pickup out of the tank. Also strange things can happen when the antisiphon valve goes.

Can you let us know a bit more about your rig? What boat and motor do you have?

 

[Maclin]

Re: How do I run out of gas before the tank is empty?

Sounds to me like the tank is not venting and the fuel pump gets vacuum locked. Try removing the main gas cap when this happens and listen for a whoosh of air going in. If it is a venting problem then loosening the main cap every so often will get you home until you can fix the venting issue.

 

[AshleysRevenge]

Re: How do I run out of gas before the tank is empty?

1982 Thunderbird Formula25 SC express, Mercruiser 8cyl Carburated

 

[Captain Caveman]

Re: How do I run out of gas before the tank is empty?

I was thinking venting too.

You mentioned changing all of the fuel lines and filters. Make sure that included not only the lines going from tank to motor but also included the fuel lines inside the motor. Those can gum up or get clogged from debris floating in your tank. If a piece of rust or junk is floating in your tank and gets sucked against the pickup outlet, that would starve your motor of fuel.

 

[ondarvr]

Re: How do I run out of gas before the tank is empty?

The pickup tube in the tank may not be mounted correctly, may not be the correct tube, or have a hole in it. This effectively makes your 80 gallon tank much smaller.

 

[AshleysRevenge]

Re: How do I run out of gas before the tank is empty?

The pickup tube in the tank may not be mounted correctly, may not be the correct tube, or have a hole in it. This effectively makes your 80 gallon tank much smaller.

Just to be sure, the pickup is from the top of the tank and has 5 screws which must be positioned properly to be replaced or reinstalled?

Everything outside of the tank except for the fill tube is new including the entire carburetor.

When I have the time I will start with that, I would like to resolve this by the weekend but well see how that goes.

David

 

[Idlespeedonly]

Re: How do I run out of gas before the tank is empty?

I doubt this is a venting issue. If it was a venting problem it would be more prone when it is full. Since this is when there is the least amount on air in the tank.
I would think possibly a bad pickup.

 

[LippCJ7]

Re: How do I run out of gas before the tank is empty?

I think the first thing I would do is take the pickup out, then drain the fuel tank completely, measure your depth to the bottom of the tank and you should have a good idea what the status is of your pickup and if you have a problem, then I would fill the tank through the pickup port not the gas port on the side of the boat, we want to know exactly how much your tank can hold, at this point go ahead and put the pickup back into the tank and go run your boat, if you don't feel comfortable keeping track of your fuel usage you can get a meter that will but they are pricey.

Here is what you know, you have a problem, you also know what size tank your boat came with, what you do not know is if your boats tank was ever replaced. So solve that first, then move on, you have to know the facts, otherwise we are all just guessing.

 

[Idlespeedonly]

Re: How do I run out of gas before the tank is empty?

Just to be sure, the pickup is from the top of the tank and has 5 screws which must be positioned properly to be replaced or reinstalled?

No, The five screws is the sending unit.
The pickup is the fitting that the fuel line connects to.
Remove the fuel line, the unscrew the fitting.It is supposed to have a siphon tube attached to it.

 

[smokeonthewater]

Re: How do I run out of gas before the tank is empty?

SOME fuel tanks will have two or more pickups and SOMETIMES one of those pickups will be shorter than the others.
The short pickup which usually won't reach the last 1/4 tank is generally for a generator.....

If you DO have more than one pickup look into this.

 

[AshleysRevenge]

Re: How do I run out of gas before the tank is empty?

To reply to the last few posts my sending unit with the 5 screws has a fuel line in it and the tank has the Original Label on it. Says
AFP products inc
Model 58-85-AF
Date April 1982 CAP GAL 85
Guage x.090 .125
Serial 8-85428

Here are some photos of what I am looking at

140511/IMG_5697.JPG

 

[Idlespeedonly]

Re: How do I run out of gas before the tank is empty?

The Big red one is the fill hose.
The one to the left of it should be the vent.
Out of the remaining to you will need to find out which is the engine supply.

 

[smokeonthewater]

Re: How do I run out of gas before the tank is empty?

do you have a generator?

the hoe going to the sending unit (5 screws) is something I've never seen before... the 3rd hose from the right SHOULD be the fuel pickup

 

[chrome dome]

Re: How do I run out of gas before the tank is empty?

it is a pain in the bum but l would drain the tank to make sure you don't have more water than fuel in the tank,
you'll need two 44 gallon tanks and a jiggler syphon hose thingee,

l had a similar problem with my saltwater moored boat, showed signs of running out of fuel after a while even though all tanks were "full"
found salt water in the fuel system, the filters ( 3 ) couldn't keep all the water out and a week later the 2 month old mercruiser had seized,

we now believe the water was getting into the tank through the vent/breather lines which didn't have a loop in them,

draining your tank is a lot cheaper than replacing a stuffed motor....and quicker,(2 months out of action now for us, our season is almost over and is still a work in progress )
it crosses that possibility of your list and gives you peace of mind

 

[GA_Boater]

Re: How do I run out of gas before the tank is empty?

Shouldn't the hose in the sender have a proper clamp on it?

 

[Home Cookin']

Re: How do I run out of gas before the tank is empty?

I'm betting on a short pick-up tube, or if not, one with a hole in it. It doesn't take much to let in enough air to stop the pumping.

And from the comment above, if you don't have a generator now, I bet there used to be one and someone hooked up its short hose to the engine by mistake.

Or here's an opposite approach: the tube is too long and has a flat bottom. Some pressure is either pushing down on the top, or bowing up the bottom of the tank, causing the tube to sit flat, make a seal and stop working. The solution is to cut the bottom of the tube at a 45* angle--which also avoids the bottom funk.

I don't know anything about inboards but would they ever have two fuel lines? If not, trouble shoot one and cap off the other.

Good call on checking the tank plate; that was going to be my first suggestion.

I'm sure there are boat owners who have shortened the pick-up to avoid the water and phase seperation in the bottom of the tank but that's just lazy if it's at half a tank--however it's smart not to go to the very bottom where the funkiness lies.

 

[81_chapparel194]

Re: How do I run out of gas before the tank is empty?

im guessing a short pick up tube. OR a pin hole in the pick up tube. had a car once that would "run out of gas" at 1/4 tank come to find out the pick up tube in the tank had a crack in it and would suck air in from the crack and pump would loose prime.. ON THE WATER STRATEGY if it had water in tank water is heavier than gas and would settle to bottom and provided the pick up tube was correct length would suck water FIRST and wouldn't even run. take a clear plastic bottle and pour half with gas then half with water let it sit and watch the water go to the bottom..

 

[AshleysRevenge]

Re: How do I run out of gas before the tank is empty?

This boat probably did have a generator at some point and yes both of the fuel lines go to the fuel water separator. Both have there own ball valve. As for the hose clamp, I believe you mean the one on the far left. It was the one that was there before, I'll be sure and change it.

Okay I've disconnected the anti syphon valve and fuel line and unscrewed the pick up tube. Refer to pic I can not remove it straight up because of the fiberglass above it. Which is a storage area. I am looking to drill a hole directly above the pickup tube in the fiber glass?

Bad idea, good idea, another Idea? Also this shows this is the original tank that came with the boat.

 

[81_chapparel194]

Re: How do I run out of gas before the tank is empty?

one of those hoses, most likely the one in the sender unit is the return line for un used fuel to go back to the tank.