Hi, My raw water cooled 2QM15 had a problem of intermitting over heating. I check and replaced many things: hoses, belts, impeller, ... I even pickled the engine with vinegar and turned over water pump impeller backing plate thinking the wear was limiting flow. I even thought I licked the problem. After a big trip (2 two-days gulf crossings), I left the boat for a few weeks and when I returned, the engine was seized. It turned out the head gasket was slightly blown which let raw water in the cylinder and over two weeks corroded/seized a piston.
I discovered the real reason for the heating problem(and likely the reason for blowing a head gasket) when I fixed the engine: severe salt scale build up! The picture below is my block with the cylinder selves removed showing what was likely 33 yrs of scale build up. http://www.flickr.com/photos/dreuge/7782378010/in/set-72157631067396554 I happily rebuilt the engine(another story) but I strongly suggest that anyone with a raw water system regularly flush the engine with a good agent like barnacle buster (and don't cheap your self by using vinegar). The $30-$50 for barnacle buster is a lot less than the $800 I spent rebuilding my yanmar. - Paul E. 1979 C&C 29 Mk1 S/V Johanna Rose Carrabelle, FL Begin forwarded message: > Date: Thu, 23 May 2013 18:00:17 -0700 > From: "Don Jonsson" <dbjons...@shaw.ca> > To: <cnc-list@cnc-list.com> > Subject: Stus-List Overheating 3GMD - the plot thickens > Message-ID: <023e01ce581a$0e7118d0$2b534a70$@ca> > Content-Type: text/plain; charset="us-ascii" > > Hi > > > > I had previously sent out a message about an overheating diesel. The > culprit, so I thought, was the knuckle going into the mixing elbow, because > generally when I cleaned it, it worked again. For a while. > > > > So I finally took of the mixing elbow and gave everything a proper cleaning. > I checked the water pump. I checked all hoses by blowing through them and > the engine. > > > > I put it all back together and it all worked and water pumped like it is > supposed to, except the water pump leaked a bit - needed a new gasket, but I > knew that and just wanted to see if it would work. Got a new gasket and put > it on. Started up and no water. > > > > I took out the thermostat and checked to see it worked - slightly corroded > but it worked, i.e. opened in hot water. Put everything back together and > started it up and a bit of water but too much steam. Took the thermostat > out and put it in more carefully. Tried again, water running, no steam > everything is perfect. Ran it for a while just to be sure. > > > > Turned it off. Waited a while (an hour) and started it up again. No water. > > > > So the problem is not the mixing elbow (and likely never was as it wasn't > that bad). Not the pump as it looks fine. Not the thermostat - I don't > think although I will replace it. > > > > The problem is sometimes the engine pumps water and sometimes not. And I'm > stumped. > > > > This is a raw water cooled engine which makes things different. Has anyone > had a similar problem and ideas for a solution. > > > > Also, it seems hard to get part numbers for a 3GMD and the local mechanic > had to go find an old book. Is there any place online to find part numbers > for that engine? > > > > Thanks to anyone that can help. > > Don > >
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