Chrysler 318 cooling issues

[nitsuj]

Hi gang. Hoping you all can help. I have a 1991 Gibson houseboat with twin 318's, v-drive. Last weekend my starboard impeller tore itself apart. It was replaced last season, so I thought maybe it was just time. Now I'm thinking it starved for water and over heated. I caught it early by not seeing water coming out of the exhaust. Boat never over heated, or even came up to operating temp. So I got a new impeller. Before installing it, I blew air out of the intake line, no blockage. (A couple vane came off the old impeller but I found them.) I also flushed the system both ways with a hose. No blockages. So I put it back together and fired it up. No water from the exhausts. I'm at a loss. I've checked and re-checked everything. I have flow everywhere with a water hose or air. Every other boat I've had, the pump is below the water line, this one, it's above the water line so I know it has to pull the water through the inlet hose, but it's not. At least not enough. It's drawing enough water to wet the insides of the lines, but not enough to get water out of the exhaust. Do I need to prime it somehow? Or pressure test the system for leaks? I've had a lot of I/O's but this is only my second season with a v-drive.

Thanks in advance.

 

[Scott Danforth]

rubber impeller pumps are only self-priming if they are below the water line.

they do not "suck" water or "pump" water, they only push water

did you backflush with water or just air. if air, you need a lot of air (as in about 500 CFM of air at high pressure (think of a pumpkin cannon) a typical air hose will not do it as there is not enough force to move things unless there is a seal like some sort of wadding

 

[nitsuj]

rubber impeller pumps are only self-priming if they are below the water line.

they do not "suck" water or "pump" water, they only push water

did you backflush with water or just air. if air, you need a lot of air (as in about 500 CFM of air at high pressure (think of a pumpkin cannon) a typical air hose will not do it as there is not enough force to move things unless there is a seal like some sort of wadding

That’s what I can’t figure out. The impeller is definitely above the water line, so I can’t figure out how to prime it. I flushed towards the engine with water and got water out of the exhaust. I flushed the line from the impeller to the through hull with air. I didn’t use 500cfm, but there was no obstruction. There was no (or very little) resistance. Any air I pushed through hose bubbled from under the boat. I used a large blower, similar to an electric leaf blower. Low pressure but high volume.

 

[Lou C]

Did you pull the thermostat housing and check for pieces of the old impeller there?

 

[nitsuj]

Did you pull the thermostat housing and check for pieces of the old impeller there?

Yes. All pieces of the old impeller are accounted for.

 

[Scott Danforth]

That’s what I can’t figure out. The impeller is definitely above the water line, so I can’t figure out how to prime it. I flushed towards the engine with water and got water out of the exhaust. I flushed the line from the impeller to the through hull with air. I didn’t use 500cfm, but there was no obstruction. There was no (or very little) resistance. Any air I pushed through hose bubbled from under the boat. I used a large blower, similar to an electric leaf blower. Low pressure but high volume.

I would hook a hose and back flush the inlet. you probably have some debris in there that allows a few bubbles, however not allowing water.

 

[Lou C]

If you are in an area where there is marine growth that can cause a blockage in your raw water intakes. Very common here with boats moored in salt water. I usually tilt my outdrive all the way up every couple of weeks to check the water intake holes.
Even if the impeller is slightly above the static water line there should be enough hydrostatic pressure to fill that hose up to the impeller, if not you would have had continual problems with the impeller not priming.

 

[kenny nunez]

Get a bucket of water and some hose connected to the intake side of the pump as close as possible, submerge the hose in the bucket and see if it draws water. Also disconnect the discharge side to see how much water comes out. I know this sounds strange but give it a try.