Bilge Pump and Siphon Problem - WARNING

Mike · **Joined:** 09 Jul 2008 12:51 **Posts:** 251

I just finished moving my boat to Gulf Shores from Grand Rivers, Ky down the Tombigbee Waterway. During the trip I would normally check the bilge and engine compartment as we motored along. I started the trip running the engine at around 1700-1800 RPM. On the 4th or 5th day I needed more speed so I increased her to about 2300 RPM. With the boat loaded down with extra fuel and "stuff" the stern really began to squat at that RPM. I checked the bilge as I normally do throughout the day and discovered I had developed a siphon problem on the bilge line. When the water pumped out the pump normally stopped but the extra water in the line and the added outside back pressure from the stern squat caused a siphon to start. It immediately filled the bilge up again and the process starting all over again. Good thing I caught it because it would have burned up the pump eventually. I noticed at a lower RPM this did not occur. I turned off the auto bilge until the end of the trip.

Since the bilge line has a loop before exit I figure that is as it should be. It's the back pressure that is the problem. I'll be adding a back flow valve in the future to prevent it from happening again.

Just a word of warning.....

Tortuga's Lie · **Joined:** 27 Oct 2006 10:32 **Posts:** 827

Where's the exit through-hull for your pump? Are you using the cockpit scupper drains? Transom?

Mike · **Joined:** 09 Jul 2008 12:51 **Posts:** 251

Not the scupper drains, higher. I'm inclined to install another through hull above engine exhaust and higher at the stern. Even if water is above it there shouldn't be the water pressure like it would be at the port/stbd at high speeds.

Poor design in my opinion.

puffcard · **Posted:** 23 Oct 2013 08:06

I know what I did won't be approved by all. I saw the same thing and added an in-line check valve to the pump discharge and has worked great. It helps with pump short cycling and back siphoning.

Tortuga's Lie · **Joined:** 27 Oct 2006 10:32 **Posts:** 827

I have a check valve on mine and yes, it does help but once the rubber inside these valves get old, it will weep back down and you'll need to replace them once in awhile. My outlet is about 6" down from the toe rail by the nav station (it shares the same space as the fuel fill hose) and I have a loop on it as well.

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Bilge Pump and Siphon Problem - WARNING

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