Half a day at the boat in 98 F heat. Most of the time in the port quarterberth and the starboard "sail locker". Lost a few pounds of water weight for sure.
Raw Water Feed Through Hull Investigation
-Removed hose after a cautious wrestling match. (Images of a sheered Marelon through hull flash in my mind.) Hose removed. A viscous clear fluid seeped out of closed through hull along with a slight smell. Probed and flushed through hull both directions. Flow was strong/symmetrical when valve opened. Had never done this before. The pressure was impressive.
https://photos.app.goo.gl/hkRtfSnh1Q8sXWoA7
-Inspected hose between through hull and garden hose T fitting.
A plug of kelp like material was found to be stubbornly set between the through hull side and the garden hose T fitting.
-Material wedged along the radius of the forward edge of the garden hose T fitting inside the feed hose.
-The kelp came out in the shape of a dense sewing thimble. More viscous fluid along with the plug.
Here is the picking tool I used inside the section of the feed hose I am referring to. The material was woven and wedged in tight.
https://photos.app.goo.gl/TkMDt8QB1q6Rhxhh8
Here is the plug after unweaving the material.
https://photos.app.goo.gl/HoMqdu3p5DHnY32Z6
https://photos.app.goo.gl/SF3a6jPdCB6NeGiLA
Checked flow from garden "T" to basket filter. Basket filter to pump.
Moyer Flange Pump and Backing Plate Leak
-Much closer inspection of impeller. No signs of cracked or compromised paddles. Replaced last July. Clear that the impeller had never run completely dry. No dry wear around top nub of paddle. No noticeable play with impeller shaft.
-Much closer inspection of backing plate
https://photos.app.goo.gl/JBvUYZ8n5JV5LnETA
Noticed radial etching on backing plate. I theorize that at some point in all this fine metal particles may have settled back between backing plate and paddles from the hose feeding the water jacket injector.
Cleaned out O ring seating groove. (confirmed no missing O ring/determined only 1 O ring used in groove).
-Marine grease in groove and on O ring. Noticed and noted a fine small flat spot on the O ring. Replaced backing plate.
-Tested cooling system. SUCCESS
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Spot checked water flow and temperature nominal relative to my history with the motor.
https://photos.app.goo.gl/dVUHbLFJCB3Hd5Gk8
Checked for backing plate leak. Lead slower but still present. Same location. Leak greatly reduced yet there is still a droplet that slowly puddles.
-Will check backing plate housing and order new O rings. See if that stops it. Confirm that backing plate lays flat, no warping or bend.
Leak during running
https://photos.app.goo.gl/MQnWFNFH4JWMrcZ36
Noted that leak when not pumping has slowed to point that no water drop pooled for at least 30 minutes after shutdown.
Choke Points and Flush
-Will still make my way around engine cooling choke points. And consider acid flush this season.
Follow-Up
-Backing plate leak.
-Pump flushing/maintenance if metal particles making way into housing.
-Concerns about Garden "T" fouling feed before strainer.
-Temperature sender and gauge repair replace.
-Look into early warning systems available.
-Water pressure, exhaust pressure, etc.
-Fresh water cooling in my future.
Thank you for all the help this far. Welcome any suggestions on pump backing plate beyond my next steps. Very productive day because of this forum, MMI flange pump documentation, and the service, rebuild, and newsletter manuals.