Fuel Overflowing Fill Tube But Cannot Pump Fuel Out.

[tperk100]

Filled her up yesterday. 50 Gal. Stopped pumping at auto cut off. Today fuel is overflowing out of fill tube. Took cap off. Fuel is all the way to the top. So my first question is why is this happening? Temp yesterday was warm, today is cool. Both days boat was level.

So I pumped the fuel out of the fill tube. My transfer pump pickup want WAY down to where it sounded like it was rattling on the bottom of tank. I pumped about 1/2 gallon of fuel and then pump would not pick up any more. I have experienced this before with other pumps and siphons...........unable to siphon the gas, EXCEPT for gas in fill tube. My second question is why is this happening? My fill tube is a combination fill and vent. Could there be something wrong with it?

Thanks for any help.

1997 Scout Sportsman
1997 Yamaha S150

[DennisG01]

Just for clarification, is the gas overflowing via the fill hose or the vent?

Check out the vent hose. If there's a low spot in it from the tank to the fill fitting, then it is full of fuel, creating a vacuum scenario as you try to remove fuel... which prevents you from doing so. Start siphoning again, but just stick the siphon hose down the fill hose a very short way. Just keep going till you get all of the fuel out of the fill hose.

It sounds like, though, that you improperly filled the tank. A boat's system, older systems especially, is different that a car's. Don't fill the tank till it auto-shuts off. You actually got lucky - some times, fuel will spill out before it shuts off. The proper way to fill the tank is to stop as soon as you hear gurgling - that means the fuel is at the top of the tank and just starting to get close to the vent line fitting at the tank. This means you need to listen closely at the fill fitting and pay attention to what's going on. In lieu of that, you could install a whistler (google it) in the vent line - it's much louder than the gurgling.

Most likely, you won't be able to run the engine, at least not for long, until you fix this - again, chances are high that it's a dipping vent line. The vent fitting could be clogged - but that's less likely with vent fitting built into the fill. Of course, there could be something that was floating around in your tank and it got lodged into the vent line, as well.

[DennisG01]

Just to add some more info...

You may or may not have a dip in the vent line... But I wanted to add that another reason you may not be able to siphon fuel out could simply be due to the siphon pump not being strong enough to lift fuel from the bottom of the tank.

Either way, get the fuel out - double check the line - disconnect the vent line from the fitting and blow it out if you want. Then don't fill up like that again!

[tperk100]

Just to add some more info...

You may or may not have a dip in the vent line... But I wanted to add that another reason you may not be able to siphon fuel out could simply be due to the siphon pump not being strong enough to lift fuel from the bottom of the tank.

Either way, get the fuel out - double check the line - disconnect the vent line from the fitting and blow it out if you want. Then don't fill up like that again!

Dennis,

Thanks for your comprehensive response. My fuel transfer pump is new, and is more than adequate. I purchased it a few weeks ago to empty tank of about 20 gal. I really like it. Here it is….

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I’ve owned 6 boats over the years and have never had a problem with fuel overflow……even when filling to full capacity. However, an old dog can learn new tricks. Just for the fun of it I read my 23 yr old operators manual and it said “Do not fill to capacity to allow for fuel expansion.” I have had this overflow “problem” for the ten years I’ve owned this boat. Lesson learned.

For clarification, when I removed fuel cap yesterday, gas was all the way to the very top overflowing both fill tube and vent. This is my vented gas fill.

https://www.westmarine.com/buy/perko...-fill--6586168

I don’t know which tube, if not both, was overflowing. I read that fuel caps for these gas fills are not vented but have valves to relieve pressure. Maybe a cap valve is not working, but I doubt it because I can pump gas into the engine. I had no problem removing all fuel from fill tube, but could not pump more from tank………...just sucked air after emptying fill tube. I’ve tried to do this a few times in the past with the same results. I’ve also put 80 lbs. of compressed air down the vent tube a couple of times with no relief. I did, however, create about a 6 ft high gasoline geyser!

I assume, as you suggested, that I have overfilled the tank. This won’t happen again. But WHY can’t I pump fuel out from the fill tube? Seems like, that even if vent was completely blocked, there would be plenty of atmospheric relief around the pump pick up hose (that does not make an air tight seal to fill tube). To empty tank of bad gas a few weeks ago, I had to remove fuel gauge sender and pump from its hole.

Today I am going to measure how much of the transfer pump hose goes into the fill tube. Then I will measure distance from cap to gas tank…..just to be sure my transfer pick up fitting is in the tank. I am also going to inspect the vent at the tank. I think I remember that it looked OK with no low spots but will check it again anyway. If not too difficult, might disconnect it and blow out from tank end, and then also probe the tank fitting for any obstructions.

BTW, even filled to full capacity the engine runs fine.

Thank again for your help. Any thoughts on any of this?

1997 Scout Sportsman
1997 Yamaha S150

[ausnoelm]

Chances are the siphon hose inlet is too deep in the tank, and the outlet is not far enough below it, you need the outlet right on the ground, and the pickup not too deep.

[DennisG01]

Chances are the siphon hose inlet is too deep in the tank, and the outlet is not far enough below it, you need the outlet right on the ground, and the pickup not too deep.

I was under the impression that he was using a powered siphon... but otherwise, yeah, physics still applies!

[tperk100]

Just to add some more info...

You may or may not have a dip in the vent line... But I wanted to add that another reason you may not be able to siphon fuel out could simply be due to the siphon pump not being strong enough to lift fuel from the bottom of the tank.

Either way, get the fuel out - double check the line - disconnect the vent line from the fitting and blow it out if you want. Then don't fill up like that again!

I tried to post this last night but the system thought it was spam and it is awaiting moderation. So, here it is again.


Dennis,

Thanks for your comprehensive response. My fuel transfer pump is new, and is more than adequate. I purchased it a few weeks ago to empty tank of about 20 gal. I really like it. Here it is….

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I’ve owned 6 boats over the years and have never had a problem with fuel overflow……even when filling to full capacity. However, an old dog can learn new tricks. Just for the fun of it I read my 23 yr old operators manual and it said “Do not fill to capacity to allow for fuel expansion.” I have had this overflow “problem” for the ten years I’ve owned this boat. Lesson learned.

For clarification, when I removed fuel cap yesterday, gas was all the way to the very top overflowing both fill tube and vent. This is my vented gas fill.

https://www.westmarine.com/buy/perko...-fill--6586168

I don’t know which tube, if not both, was overflowing. I read that fuel caps for these gas fills are not vented but have valves to relieve pressure. Maybe a valve is not working??? I had no problem removing all fuel from fill tube, but could not pump more from tank………...just sucked air after emptying fill tube. I’ve tried to do this a few times in the past with the same results. I’ve also put 80 lbs. of compressed air down the vent tube a couple of times with no relief. I did, however, create about a 6 ft high gasoline geyser!

I assume, as you suggested, that I have overfilled the tank. This won’t happen again. But WHY can’t I pump fuel out from the fill tube? Seems like, that even if vent was completely blocked, there would be plenty of atmospheric relief around the pump pick up hose (that does not make an air tight seal to fill tube). To empty tank of bad gas a few weeks ago, I had to remove fuel gauge sender and pump from its hole.

Today I am going to measure how much of the transfer pump hose goes into the fill tube. Then I will measure distance from cap to gas tank…..just to be sure my transfer pick up fitting is in the tank. I am also going to inspect the vent at the tank. I think I remember that it looked OK with no low spots but will check it again anyway. If not too difficult, might disconnect it and blow out from tank end, and then also probe the tank fitting for any obstructions.

BTW, even filled to full capacity the engine runs fine.

Thank again for your help. Any thoughts on any of this?

[DennisG01]

Hi Tom... OK, I see where you're coming from better, now.

Yes, trust me about not filling all the way up! Been there, done that, bad things happen. I'm also "in the business" so have heard of this issue many times. Listen for the "gurgle"! It definitely "can" affect the engine running - but there's a bunch of variables at play as to whether or not it WILL affect the engine running properly.

This: "just sucked air after emptying fill tube", I think, gives us a clue as why you can't suck fuel out. Especially since you now said you were able to siphon the fuel out of the hose, but no more. Did I understand that correctly? Assuming "yes"... It sounds like the siphon hose is only going down as far as the top of the tank. There very well could be a "blocker" built into the tank nipple to prevent someone from stealing your gas. So, at that point, the "air" was coming from the little bit of air gap from the top of tank and the vent line and/or just the air space now in the fill line.

You could use the fuel pickup fitting on the tank (although you need a siphon with enough force to overcome the anti-siphon valve in the pickup... assuming you have an AS valve). Or, as you did before, remove the sender plate.

Now... why did the fuel expand so much? Here's what "I think" happened.... bear with me, this might be long... you mentioned "temperatures" and ambient temp's can certainly have an impact. But, there's also "fuel" temperatures. Meaning, the fuel you pumped in came from underground and was likely much colder than ambient. So, you ended up with an air bubble in the tank - probably due to the angle the boat was sitting at and this air bubble was at the opposite end of the tank than the fill/vent nipples, so it wasn't able to escape. As the fuel then warmed up, things expanded and there was nowhere for this extra pressure to go except to push the fuel out the only opening available. If the tank wasn't overfilled, this most likely would not have happened... unless the boat is stored at an extreme angle where things still get blocked.

[99yam40]

$190.00 transfer pump should pump until there is no more liquid the pick up tube reaches, so nothing to do with siphoning

[zenoahphobic]

I am just wondering that your siphon tube maybe curling up. I am sure almost everybody has had this happen at some time, and have actually been able to see this, when “over inserting” the tube hits the bottom or a curve on the side and starts to travel in a different direction deflecting as it goes and eventually heads upwards. I often over the years have this happen being alerted by the apparent length of the tube inserted seeming more than the depth of the tank.
To check this insert a solid rod till it hits the “bottom” and mark it off and extract it. If it looks too short your tank is irregular or has some type of blockage or baffle in the way. If it looks right you can always tie (not tape) the siphon tube to this rod and then insert. (Even tie the end a little higher to stop it hitting or sucking onto the bottom, blocking it).

[tperk100]

Guys,

It turns out that these “problems” I’ve dealt with regularly over the last 10 years are NOT problems at all. There is nothing wrong with my boat’s fuel system or my transfer pump….only with my boat’s owner.

I realize now that I have overfilled the tank, and that overflow should be expected if filled to capacity. My 50 gal tank, if full, can expand by over a gallon’s volume in hot weather.

I realize now that the fill tube makes a 90 degree turn at the tank with a metal fitting, and that my transfer pump’s suction line fitting will not go through the turn. This is what my pump’s suction line fitting was rattling against…..not the innards of the tank. This is why I can only pump gas that is in the fill tube.

I know now that I’ve spent many frustrating hours dealing with problems that existed only in my mind. You would think a guy with 40 yrs of boating experience would know better.

Thanks for straitening me out.

[DennisG01]

Hey, at least it was a "freebie" fix! We don't get those all that often when working around boats!

Don't beat yourself up - you don't know till you know... you know?

The "gurgle"... depending on ambient noise, you have to get your ear pretty close to the fill... and as the years go by, you have to get closer and closer It doesn't take much time after you hear the gurgle for the gurgle to stop... which will then very quickly give you a repeat of that gas geyser you experienced previously! So... STOP when you hear the gurgle. And check out that whistler - it works really well.

[tperk100]

I checked on the whistler yesterday and found this.

https://www.defender.com/product.jsp?id=848503

Would like to have one but considering that I fill my boat up about 2 times per year (most fishing trips are very close in and in no wake zones), and that I don't want to be upside down and contorted in my bilge trying to install the thing, I am going to pass. Believe me, even with my evasive 70 yr old memory, I will not forget to avoid filling to capacity in the future. And yes, must get closer and closer as years go by. This is me at the gas station now..............

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