Impeller Problem
 

I burned out my starboard impeller yesterday. I have burned out my port impeller three times this year. :(

I think the problem occurs when I put the boat on my lift. When I raise the boat, the water drains out. When I lower the boat back into the water, there is still air in the lines. The boat sits high in the water and the seawater pump is above the water line.

The impellers run "dry" for a few seconds until the line is full of water. After a few times of this, the impellor fails.

To try and circumvent the problem, I plan to prime the water line by connecting a garden hose and "flushing" the engines after I lower the boat into the water and just before I start them.

As anyone else experienced this problem?

Do you think that Run Dry Impellers will fix my problem?

As mentioned in the GD, the run dry impellers do not flow as much water as the stock Mercury units. Hence, your running temps may be up 10-15 degrees.

Even though your outdrives drain when lifted, your plumbing from the transom to the SWP should not. Is this hose/plumbing level, or tilted fore or aft (when the boat is on your lift)?

Perhaps you can open the blue freeze plug drain on the SWP when you first lower the boat into the water. This ought to allow the air to be pushed/bled out, and water to push up from the transom assembly/outdrive.

Not sure why, but seems you must have some other kind of problem going on. My boat sits on a lift long periods of time and only have to change the impellers on a regular maintenance schedule. You might have to talk to someone that is more of a mechanic.

Also, have heard those "blue" run dry impellers don't flow the water, so not sure about them. In your case they may be the answer tho.

Good luck.

While the boat was sitting in the water, I disconnected the intake line from the seawater pump. Some water flowed in, but it was a weak stream. I thought I had a constriction in the line, but the problem has now occurred on both engines. I think that the boat sits high in the water and the seawater pumps are above (or right at) the water line.

I like to keep my gas tanks under half full so that it runs faster. Maybe I just need to keep my tanks full so that the boat sits lower! :D

are you putting any type of grease around the housing before you install the new impellers?

No

I've trailered my boats every weekend for years and have never had that problem. I'd say you do have a restriction, If I pull the water line off my seawater pump (no strainers) I get a fire plug worth of water coming in!!!!

You shouldn't use grease on the impeller install. When installing a new impeller, use liquid dishsoap as a lubricant..................

..........or in Clay's case, he could use some of the KY he's got on the boat:D:D

I've always heard to use SOME kind of lubricant. I wasn't necessarily referring to wheel bearing grease. :) Just something to coat the housing.

The grease is for installation and initial start up after a few minutes or hours its all gone. Have the motors been running hot? There must be something happening to cause that many failures. Did you replace the housings with the impellers?
Jim