[C320-list] Overheating

[Bruce]

While the impeller maybe fine maybe the back or inner face of the pump is worn and hence not always able to prime the pump leading to the low or no flow.  Also there is an insert in the pump (can't recall what it is called) that is usually replacable.  If this is worn then both the amount of water and the amount of vacume it can pull to prime the pump is reduced.  I assume the pump is not leaking.
I had a similar problem and found that when I cut the ty wraps that held the intake (to the pump) hose up and then lowered the hose as low as I could the pump move a lot more water.  I ended up taking the cover off and using a sanding disk removed the scratches.  Kept moving to finer and finer sand paper and then the last step was to polish it.  After that I was able to put the hose back to its original position and it has woorked fine ever since.
Bruce
Somerset 741 Dana Point

Bruce Heyman 
949-289-8400

-----Original message-----
From: Jack McDonough <mcdonough5 at verizon.net>
To: C320-List at Catalina320.com
Sent: Mon, Aug 15, 2011 12:47:20 GMT+00:00
Subject: [C320-list] Overheating

A puzzling, intermittent overheating problem developed a couple of weeks ago with the 3GM30F Yanmar in my 2003 C-320.

While traveling at low speed from an anchorage to a newly available mooring one morning (maybe 10 - 15 minutes running time), the engine overheat alarm sounded. I managed to pick up the mooring, after which I pulled the raw water intake hose at the seacock and determined that water was, in fact, coming into the system. I then checked to see that the strainer was clear and, finally, took apart the impeller housing and inspected the impeller -- which was newly installed in May and which looked fine. I started the engine again and still got only steam out of the exhaust. A couple of tries later, however, the system once again pumped out water like a champ. 

I made a three-hour passage to another harbor under power the next day and everything was fine -- but the same problem occurred the following day. Again it blew steam -- but the following morning I got a healthy flow of water and headed home.

Since then, I have again pulled the hose off the intake seacock but, this time, I took my digital wire coat hanger and fed it down through the intake passage to make sure there was nothing flopping around in there. I disconnected the other end of the hose -- at the strainer -- and detemined that there was nothing in the hose. Then I removed the hose between the strainer and the impeller and confirmed that it, too, was clear. 

I have a sense that I'm more likely to be able to pump water if I briefly goose the RPMs up to 2000 or a little more. But I've consulted my diesel guy and he says that shouldn't make any difference. It should pump water regardless. 

That's my story. Any ideas?

Jack
#947