[C320-list] Overheating

[Jack McDonough]

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