FW pump not priming?

midexp

midexp

Active Member
Oct 5, 2016
423
Harrison Township, Michigan Lake St.Clair
Boat Info
1999 40' Sundancer
Engines
454 merc
My new FW pump seems to have a hard time sucking up the water from the FW tank (that’s why I replaced the old one). The hose coming out of the FW tank runs along the floor of my bilge (tank is not accessible. Somewhere midship on port side) and stops just beyond the bulkhead separating the cabin from the bilge. From there, it takes a 90 deg. bend and connects to the pump suction side about 2 ½ feet up. When I disconnect the hose coming from the FW tank at the elbow connecting it to the pump, no water comes out. Which implies my FW pump has to suck the water from the hose connecting to the tank. Does anyone know if the water from the FW tank should have enough pressure head from the height of the water level in the tank so that water should flow out without having to get sucked out by the pump? Not sure if my question makes sense? In other words, if I disconnected the hose coming from the FW tank, would it drain out on its own?

Or could there be a vent that's plugged which is why the FW tank doesn't drain? I stuck wire in the small vent on the side of the hull and didn't find anything like lint or spiders.

Thanks


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What do you mean by 'seems to have a hard time'? No water at all, lite flow, spittin' an sputterin'?
The pickup tube in the tank goes in from the top. If you unhook that line at the pump water would not flow on it's own. Did you try blowing back into the tank? Are you sure there no problem on the output side that restricts the flow? Did it ever work correctly, new or old pump? If you fill the water tank plumb full does it work better?
 
How old is your fresh water pump?

If it runs and doesn't prime I bet the farm your diaphragms are bad/hardened and need to be replaced.

You can buy the entire head unit and replace in a few minutes.

I had to do this a few years ago.
 
He said that the pump is new, but is having the same problem as the old one. The pickup tube would be my first place to look. It could be all crusted up or even have holes in it sucking air.
 
Thanks for the replies. I tried unscrewing the filter with the pump running thinking water would spray out all over the place but there really wasn't much water being sucked in from the pump. As was noted, pump is new so I doubt both the previous pump and this one is bad. If I remove the line coming from the tank and place it in a bucket full of water, it sucks the water into the pump fine. As far as looking at the pickup, assuming you mean the tank pickup, I can't even see the FW tank to be able to check that. There are times the pump does come on, reach pressure and shut off. It is common that I get a lot of what looks like air burst when the water is flowing out of the faucets. I just wonder if it's normal to not have any water coming out of the hose that comes right from the FW tank if it is disconnected? And I may try blowing some compressed air back into the FW tank line. It seems like the pump isn't getting water from the tank enough to prime it all the time.
 
We have had air get in our system between the tank and the pump. When that happens we turn one tap on and off for a few seconds until the pump primes. Our pump will not prime unless a tap is open and closed. Also the screen filter has a screw on the bottom. I tool it out and put a small O-Ring on it. I put Plumber paste silicone on the O-Ring on the filter where it screws into the body. Any air leak we found will cause the system not to work.
 
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Have you ruled out an obstruction in the hose itself? Depending on how diligent you have been keeping the water tank free of microbes, fresh water slime could be plugging up the hose.
 
I don't know if it matters or not, but every pump that I've installed, the manufacturer's installation directions says "If mounted vertically the motor should be above the pump head"...

Good luck!
 
Yes tried with fill cap off, still no water getting to pump. As far as pump mounting location in relation to pump head, I'm assuming the pump is mounting where Searay installed it and it was working fine when new, But perhaps the PO relocated it? Guess I need to find out on other 1999 40 DA's where their pump is. Good suggestion. Not sure how a screw in the bottom of the filter would cause this, but I'll check.
 
midexp said:
Guess I need to find out on other 1999 40 DA's where their pump is
Click to expand...
Greg your pump is located right where mine is. I would say it has not been relocated. Are you going to be at the boat tomorrow (Sunday)? I will be there tomorrow and we can compare everything.
 
Greg I just remembered that I took a pic of mine. I don't know if this is your problem or not but it appears your pump is mounted upside down compared to mine. Here's a picture of mine.
20180528_091029.jpg
 
Just for poops and giggles why don't you eliminate the screen filter that is in between the pump and tank and see if it primes.
You said you tried unscrewing the filter with pump running but water did not spray out--it will never spray out on that side of the pump. It is the suction side meaning it is under a vacuum not under pressure. The slightest leak around that filter or any other connections on that side of the pump and it will not pump any water with the air coming in.
 
Good point Sub I did that when mine had problems and it worked. I then made sure the filters were air tight and put them back in
 
I am having an issue where one of the fresh water pumps on my 400 Sedan Bridge will not shut off. My boat is equipped with two pumps in line and one shuts down after the lines reach preset pressure but the other will keep running.

I have replaced the pump twice and tried without the screen filter. There are no leaks at the pump and I have tried each pump independently by turning off 12v breaker at panel and they behave the same. The one that runs constantly will provide adequate pressure at the fixtures.

Am I missing something?
 
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