Originally Posted by casey1999
Did not have time to work on engine yesterday (but I did get the AC to work on my 87 bmw 325e after many hours of trying to figure out the wiring when using 5 different wiring diagrams that are all supposed to be for the same car- turned out to be a bad unloader relay).
I will work on the yanmar on Friday evening. Plan to first make sure all hoses and passages are clear and then will move to the impeller. Have heard stories the impeller (even a new one) can spin on the shaft. I did load up the impeller with silicone grease prior to install. I had greased the one I removed with a water proof grease and it looked almost new when I removed it (been in service for 2 years). FWIW I had accidentaly run the engine a couple times without the seawater valve opened for several minutes about a year ago and about 6 months ago, and it apparently did not hurt the impeller- I try not to do this but mistakes happen. I use genuine yanmar impellers. I will stick to the water proof grease as this does seem to help save an impeller.
If my silicon grease, you mean the sticky stuff in a tube, that may not be a great idea. It should certainly help prime the pump, but I would worry what happens to it as globs move through the heat exchanger or block. Glycerin or dish soap, which are less viscous, are the norms.
Running the impeller dry will do damage, even if you can't see it with the naked eye. The vanes could let go on the next run. Best to always replace an impeller that you know you ran dry for more than a few seconds to prime.
Could be a blocked intake, but it would be very unusual. Blockages in the exchanger are more common. Or, as I said, if the seawater strainer has a leak, it may not allow for the suction necessary to draw the raw water.