Air being sucked violently through fuel / water separator?

[BoatGraphicsPR]

Good morning, everyone. I went on a long trip, and on the way back my port engine wouldn't go past 3900 RPM. By the time I got into the marina, this engine shut off. I opened the drain plug on the water separator (Racor S3213), and instead of the thing draining, it started sucking air like crazy. After that I've only used the boat for short trips, and the the problem remains. Now its happening when I open the plugs on the water separators for both engines. Any ideas as to what could be causing this?

Thanks,
Felix

 

[SkunkBoat]

Re: Air being sucked violently through fuel / water separato

first guess is that the fuel is running back to the tank.
Do you have fuel shut off valves and did you close them before trying to drain the filter bowl?

 

[max366]

Re: Air being sucked violently through fuel / water separato

Could be a blocked fuel tank vent causing a vacuum in the tank as the fuel is withdrawn. Would explain the engine issue (will pump fuel ok initially but the problem gets worse as more fuel is used and the engine gets starved). When you opened the drain valve, it relieved the vacuum by sucking in air.

 

[BoatGraphicsPR]

Re: Air being sucked violently through fuel / water separato

first guess is that the fuel is running back to the tank.
Do you have fuel shut off valves and did you close them before trying to drain the filter bowl?

Good afternoon. I do have fuel shutoff valves, but no, I did not shut them before trying to empty the bowl. I don't really use them at all, really.

Thanks!

 

[BoatGraphicsPR]

Re: Air being sucked violently through fuel / water separato

Could be a blocked fuel tank vent causing a vacuum in the tank as the fuel is withdrawn. Would explain the engine issue (will pump fuel ok initially but the problem gets worse as more fuel is used and the engine gets starved). When you opened the drain valve, it relieved the vacuum by sucking in air.

Makes perfect sense. So this blockage would be in the tank itself, yes?

 

[wspitler]

Re: Air being sucked violently through fuel / water separato

All tanks have a vent, either out the side of the hull or incorporated in the filler. An easy way to test if that is the problem is to open or crack the fuel cap and provide a positive vent. If that solves the problem, look for a blockage, most likely insects on the vent screen. Good Luck!

 

[BoatGraphicsPR]

Re: Air being sucked violently through fuel / water separato

All tanks have a vent, either out the side of the hull or incorporated in the filler. An easy way to test if that is the problem is to open or crack the fuel cap and provide a positive vent. If that solves the problem, look for a blockage, most likely insects on the vent screen. Good Luck!

Aha! Now that you mention the vent incorporated in the filler, I realize that I've never noticed a vent on the side of the hull. I think I know what happened. When I was leaving Virgin Gorda back in February, my fuel cap fell in the drink. The guy at the marina just pulled a holding tank cap off an old Viking that they raised after Hurricane Irma. The problem began on that day. Next time I use the boat I'm going to briefly try to drain the cup. If I get suction, I'm going to close it, remove the fuel cap, and after the pressure equalizes, I will once again drain the cup to see what happens. But I think that's it!

Thanks everyone!

 

[seasick]

Re: Air being sucked violently through fuel / water separato

All tanks have a vent, either out the side of the hull or incorporated in the filler. An easy way to test if that is the problem is to open or crack the fuel cap and provide a positive vent. If that solves the problem, look for a blockage, most likely insects on the vent screen. Good Luck!

Aha! Now that you mention the vent incorporated in the filler, I realize that I've never noticed a vent on the side of the hull. I think I know what happened. When I was leaving Virgin Gorda back in February, my fuel cap fell in the drink. The guy at the marina just pulled a holding tank cap off an old Viking that they raised after Hurricane Irma. The problem began on that day. Next time I use the boat I'm going to briefly try to drain the cup. If I get suction, I'm going to close it, remove the fuel cap, and after the pressure equalizes, I will once again drain the cup to see what happens. But I think that's it!

Thanks everyone!

It is. The correct cap has a venting valve in the cap itself, The cap the marina gave you doesn't. Don't even bother testing, you need the correct fill cap.

One thing to note is that when the motor got starved for gas, it may have been providing a too lean mixture. That can cause detonation and depending on the motor, that could cause damage.