thermostat sticking closed or failed water pump - how to determine

[brooksk]

A simple question but I'm brain dead right now. Fired up my 5.0L GL-D engine yesterday, noticed water dripping from the impeller housing area. First time it has ever leaked there. Ran motor for 15-20min at ~1000 rpm (wouldn't idle any lower) until engine temp hot enough to open thermostat - which should be ~160 degrees. Last summer saw a few readings on the temp gauge go over 180. Am wondering if the thermostat is sticking closed. How to tell if its just thermostat vs. water pump? I felt the hoses and only the big line from the themostat housing was hot. All other lines were cool. I was not on the water - at home with garden hoses attached to both intake and engine flush port. I will change out the impeller but not sure if that's enough. Any advise?
Boat: 2004 Chaparral 215 SSI, Volvo-penta 5.0L GL-D, 147hrs.

 

[dypcdiver]

Unless hoses or the screws are slack on the raw water pump the only other place it can leak is the seal between the pump and bearing. Rebuild the pump with bearing, seal and new impeller, then test the engine again. A leaking seal can suck air and cause the problems you have.

See here for how to rebuild pump https://www.youtube.com/watch?v=ICtuz8nnbeY

 

[Boaterguy05]

If it was me, along with doing the above, also change the thermostat. Why would you rebuild the pump and NOT change the thermostat? It is relatively inexpensive and easy to do. Take the old one out, put it in a pot of water, turn on the stove, and you will be able to see if it opens or not.