Fresh water pump not circulating

[Earle]

94 ski Nautique w 351 Ford PCM. Not drawing water through fresh water pump. Replaced the impeller after last one shredded, but still not pumping. No clog at hull intake, no rubber bits clogged at thermostat, most hoses are checked and appear clear. I even put the impeller housing on “backwards” to check. Any suggestions?

[tomsyckn]

Does that version of the 351 have a clear freshwater strainer?
If so check the O-ring / housing for cracks.
We had an issue on our GT-40 (95' Super Sport) where the fresh water strainer had an air leak and vapor locked the intake system.... in our case at idle, just sitting we would start to overheat, but under power - when water got forced into the system and would prime it the issue went away.

... we ultimately just removed the strainer and ran straight from the intake to the impeller housing.

[SilentSeven]

Common problem with lack of flow are loose clamps, etc on the suction side of the raw water intake. Leaks let air into the system instead of drawing water. Like the poster above says, check the strainer and then check the clamps and hoses to the pump as well.

[Tom_H]

Like said above, check the intake side for air leaks. The strainer is the most likely culprit. And I assume the through-hull valve (if you have one is open). If all that checks out, sometimes they need a little neutral rev at the initial start after an impeller replacement to draw/prime. If you've done much for dry running, the new impeller could also be shot. Last possibility is that you just ended up with a bum impeller off the get-go (the impeller hub may have separated from the rubber, with only the hub spinning while the rubber stays stationary).

[bturner]

Agree with the air leak suggestions. Aside from those, on a boat that old I would also start looking at the hoses again. I've seen them delaminate on the inside and collapse internally.

Then there's the reduce to the ridiculous method to trouble shoot the problem.

Buy some clear plastic reinforced tubing from HD that's the same size as the hose attach to the input side of the raw water pump. Disconnect the hose at the source end of the pump, connect the clear plastic tubing to the input side of the pump and place the lose end into a 5 gallon bucket as close as you can get to the engine. Start and run the boat briefly, did it suck up the water? If so you know you have an issue on the source side. If not disconnect the hose on the engine side and try again. If you get flow now your issue is with an obstruction past the pump blocking the water flow. If not, you have a bad impeller (as stated above) or loose pully or broken shaft. Basically a bad pump. This can be a bit messy but it will quickly tell you where the problem is.

[Earle]

Thanks everyone for all of the suggestions. I did look at the fresh water strainer and the gasket was missing, so I replaced it and hopefully that’ll fix the problem and if not, I’m going to further diagnose it based on everyone’s suggestions here. Thank you again!

[shag]

It's easy to lose those little rubber gaskets... I usually keep 1-2 extra in a ziplock bag in the boat..