R21 Sea strainer / impeller / raw water query...

[sheral]

Just trying to figure something out here...

Finally popped the boat in yesterday (due to having been visiting family etc). I had a new impeller in place, had run fresh water into the strainer basket, and ran the engine to ensure everything was working / pumping correctly.

Raw water intake petcock was closed. Drove to the launch. Submerged the boat (intake in the chuck). Opened the petcock and tapped the sea strainer lid to ensure it was full of water. Started the engine and the impeller was not pumping water out the exhaust. Shut it down, rechecked the petcock, refilled the strainer etc. and finally after several / numerous attempts the impeller began pumping.

So my question is (I even pulled the boat out and checked the intake to ensure there wasn’t any weeds etc blocking it)... these pumps are self-priming aren’t they? Can you think of what was up here? Air lock?

And in thinking about this, the suction / pull of water up from the raw water intake is based on suction right? So if my strainer lid wasn’t on tight enough that could prevent water from being pulled in? Thoughts? Thanks.

 

[baz]

Well, first off, you did the right thing shutting engine down when seeing no water out the exhaust port.

From what you've described you did all things I would have done. It obviously does take several starts to get the raw water cooling primed to the point the impeller can take over and start pumping.

Yes, suction is how the raw water is drawn up and into the impeller pump housing.

 

[LAKERtoo]

.. I had that experience my first summer at the boat launch and hauled the boat home .. phoned my go-to guy and he laughed !! .. advance the throttle in neutral a bit ( mine you just grab the base of the throttle and pull towards you) .. he explained that you have to fill the system, including the water muffler, before you see water exhausting, even if your impellor is wet .. what I have learned to do when I haul the boat out, is to shut the seacock once the boat is on the trailer but still in the water, and the whole system shud stay primed if all your clamps are all tight .. if I've had the boat in the driveway for awhile, I hook up a short length of hose to the fitting just ahead of the sea pump / impellor and a five gallon bucket with the garden hose keeping it filled (sea cock closed) and run the motor for a few minutes to prime everything … remember to open the seacock once your boat is in the water .. Rob

 

[Newf]

I have my 21ec in and out of the salt chuck 2 to 3 times a week and have not had to wait any more than 5 to 10 sec before it's pumping water. I have started to flush system with fresh water after most uses and after "every" use I drain the water out of the exhaust elbow. Have not had a problem self priming on start-up.

 

[Capt’nKarl]

When first starting the engine it’s not unusual to have to wait 5-15 seconds before you see water being discharged from the exhaust (of course you have to have the sea cock open). The length of time you wait before you see water spurting from the exhaust depends on how long it’s been since the engine was last started. We usually keep our Tug in salt water for days and sometimes weeks at a time between outings so when we do get back to the slip I always close the raw water intake and flush the system with fresh water. Even though the raw water system is primed it still may take several seconds to see water exiting. I check the impeller blades and water pump belt often to make sure everything is working properly. I’ve had the unfortunate situation where the pump belt was too loose and slipping resulting in poor performance.
Cheers,
Karl

 

[Jubilee]

All the above suggestions are good but another thing I had trouble with was the "O" ring at the base of the water strainer cover. Without a proper seal you can have a problem with the suction necessary to pump water. Be sure this "O" ring is doing its job! A replacement is very cheap and easy to install. I solved a water flow problem this way.