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Discussion Starter · #1 ·
What would cause a water pump NOT to pump water every time? This is happen with boat in the water and connected to garden hose.

Some background info, 500 hours on 2002 496 MAG. I have changed the impellor 4 times over the last 6 six year without any problem. This time I changed it much like before and ran it on the hose after. Everything looked good so I wrap it up and called it a night. A week later I head to the Marina to go boating. (Boat is stored indoors at Marina) Put boat in water and I fire it up. As I’m loading the kids and cooler I notice no water coming out the exhaust tips. So I shut it down. After double checking that I reconnected everything correctly tried it again and still no water. :mad: :mad:

So I unload the kids & cooler and send them home with the wife and have the Marina move boat to maintenance rack. Connected it to the hose still no water out exhaust. So I remove the water pump and double check everything, flush the system with pump out to make sure nothing is clogging in the system. All clear! Reconnect everything and fire up on hose it’s pumping water out the exhaust. Let it run for 10 minutes and shut it down. Waited 15 minutes and fired it back up and it’s not pumping. :confused: :confused: :confused:

I have since removed pump again, replaced impellor with another new one, Inspected the pump housing for abnormal wear, changed serpentine belt, and I'm still having this problem. I also asked the marina maintenance shop to look at it and they just called to tell me everything looks good, they fired it up on the hose without any problems. So now I’m all confused! I’m headed to Marina after work to try it myself, Again!!

Keep in mind that the impellor I replaced was completely intact. I would not have replace it except it had some cracks developing and it was two years old!

All this in the name of preventive maintenance, well it’s preventing me from boating now!!!
 

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Sounds like the pump isn't always priming and you are getting air pockets.

Myself I have found that at the beginning of the year after everything has drained down all winter I usually have to pull off the intake hose to the water pump (after the boat is in the water) and let it fill up with water and then when the water starts coming out try and 'shoot' some water in the pump before putting the hose back on and tightening the clamp. Usually have to do the same thing whenever I change an impeller.

Do you have hi or low water pickups in the drive? If you have hi-water pickups I have also found the cheapest water-muffs work the best (that is if you are pulling the water through the drive).
 

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I had a bad gasket between plastic housing and main body that did the same thing basically . Didn't leak water thru it - you figure ?

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Speaking of which, make sure the hoses are on correct nipple and they are clamped on correctly. If there is air going to inlet of sea water pump it will pull mostly air.

Same with hose connection at inside transom assembly.

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Check oil cooler water entrance to make sure there isn't a pile of poo stuck against the small tubes that look like a screen.
 

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Discussion Starter · #4 ·
Just got back from the Marina and this is what I found out.

The service guy put the boat in the water and started the motor. No water pumping out exhaust so he shut it down. Double checked that everything was connected correct and it was. He then used the little air pump that comes with the 496. The pump that you use when winterizing the motor. After letting all the water drain he closed the drains and started the motor up again. This time after about 30 second it started coming out the exhaust.

When I got to the Marina I had them put the boat back in the water and I fired it up. No water pumping!!! The owner Marina owner was standing next to me. We did the same thing as the service guy, used the little air pump and let the water drain. We than fired it up again and after about 30 second water started coming out the Exhaust. We let it run to bring it up to temperature (150 degrees) and shut it down and restarted many times and each time it pumped with no problems.

This is my thinking. when w take the boat out of the water the water between the pump intake and out drive drains out. So this space fills with air and when we put it back in the water we created an air pocket. With that said. When we start the motor the pump must be worn out enough NOT to be able to push the air pocket out. When we use the air pump and drain the motor we reduce the head on the pump allowing it to push the air out and prime itself.

Make sense?
 
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