Sea water mystery

I have been trying to get my sea water pump in my 75 SW 18 working.
All good on garden hose.
Took it to the lake, and no sea water will enter the port and hose leading to the pump. I know this because I installed a clear hose that I can see what’s going on. So after half an hour of messing around at the dock, never got any seawater in that hose at all. I was tempted to remove the hose and see what happened when I opened up an inch and a quarter hole in the hull. I am sure Water would have gushed in. Not wanting to sink the boat. I took it home. I learned in school but water seeks it’s own level. If that were the case, then that Hose would fill up and to my calculations the pump also. This is a DV so the pump is pretty far down below water level. I have read all the forums to tell me to check everything for vacuum, leaks, etc. I have done this many times to no avail. Even if I have a bad pump, why does water not enter that hose. Tomorrow I am taking the boat to my pond and putting a different hose on the inlet to see how far up the water comes. I’m willing to bet it seeks it’s own level somewhere just below the floor,
I am at wits end. Can someone help?

I will try to answer all your questions.
The pump is in OMC belt driven mounted underneath fuel pump on the right hand side of a small block Chevy 307. I have had to pump off and rebuild it to the best of my ability as the only part available is the impeller. That means that I had to make the gaskets polish the stainless steel parts up, purchased a new bearing and seal. We are pretty capable of doing this rebuild as my next-door neighbor has a machine shop in his garage. Installed a new clear hose from the boat intake to the pump. Everything is sealed up really well there. I’m confident there’s no leaks , as for running it on the driveway with the garden hose. Yes, we are forcing the water in. I can actually force water through the pump when the engine is not running all the way through the engine and out the exhaust which would lead me to believe that Air would also bleed through the entire system and that’s why I can’t understand the water does not enter this pipe to the pump . I just read how to post pictures on this forum. I am using an iPhone, and apparently the icons don’t appear on an iPhone at the top of the page. I was very careful not to overheat the pump and ruin the new impeller when there’s no water going into it at the lake. Although this could have happened. I am not sure what my next move is as I hate to take the pump a part to check the impeller as I will have to make new gaskets again. I am thinking of just getting a new pump which I found a guy had some pieces left over but he wants a fortune for them. Like a Thousand dollars for the pump. At this point, I am willing to try anything. Unfortunately, there’s not room in front of the crankshaft to mount that style of pump. I have also located supposed replacement pump for this online is a brand new stainless steel version. That would run me about 600 bucks. As you know the condition, this boat is in right now is not worth much without new flooring stringers. That’s why I was hoping to see mechanically how fit it was before doing all that this winter. I was hoping to keep the boat original, and for what I have invested right now I could easily find another one. I had a 77 just like this and that is why I am partial to this one. The 77, was a 351.

I just had a thought. What pump do all the 351s running around here use? Certainly there’s a belt driven pump that I could convert to in OMC?

If you rebuild that pump with the impeller blades facing the wrong direction, it probably will not draw water. If it’s the same pump I have, you cannot mount them incorrectly to the block.

Assembling the pump can be hard but if you apply some wet dish soap, I use dawn, to the blades they will slip easy as you install and you can rotate them as needed for assembly.   I have installed a pump upside down and for absolute fact they do not pump water upside down but bolt right up just fine.   When we say upside down, when the pump is apart the body can be rotated so the inlet is on the bottom and the outlet on the top while all the mounting bolts are in the right position to assemble.   Worth a check.

With the boat floating in the water, we do not get any water into the hose leading to the pump from the fresh water intake. Also tried switching the In-N-Out same result. So we loosened the clamp at the pump and allowed air to bleed out and that line to fill full of water. Started the boat still did not pump water. Did this with the lines switched and not switched. I am at a total loss right now. It seems the pump does not pump. I guess I will take it out. may be bench test it. Then take it apart.
I have talked to a fellow at Northwood marina, who rebuilds pumps for Chris, Kraft and older boats. He seems to think these pumps are very complicated and he can be the only one to possibly get it to work. That route would still cost me over $1000. This is not rocket science. It’s an old boat that needs a belt driven pump. Help ! Getting discouraged.

I am in Rittman, 44270. It is close to Wadsworth.

Thanks for everyone’s help. Here is what we did last. Put the boat back in the pond floating on the trailer. Tried it again and there was no water in the hose. Remember it’s clear so I can see. Did it both ways switching the In-N-Out hose.
That did not work. So we loosened the hose at the pump, allowing the hose to fill up. And try to start the boat and it still did not pump water. Tried that with the hose both ways. In for Out out for in.
At this point, I have to assume my pump is no good.

Ken, Den sent me pictures of his pump and it is identical to the ones I have. I have one an unassembled one that would be a direct bolt on but I’m not sure of its internal condition. Seems to drag well. Worth a shot!

Haven't read the whole post.   But kinda sounds like to me that you have a dead mouse or mud dobbers in your thru-hull.

So,   If your pump is before the cooler, it's full of black rubber particles.   Pump after cooler, it's full of lake debris.   Thankfully no mouse.

Thanks for the answer. Going to look into that next.

Den’s working on it but did say the pump I gave him works. His cooling system has the rwp sending water through the trans cooler to the exhaust risers and then back through the exhaust manifolds to the thermostat housing. My Omc goes through the same pump, cooler and then directly to the thermostat housing. His is an earlier version. He did mention his thermostat was stuck so there’s more to come.

I'd fire that thing up with no thermostat just to see if you have flow.............for testing