This is info for those who have not experienced this and a reminder for those who have. I started up my Yanmar 3GM30 after a 3 week layoff, it started fine, but I was not getting much water thru the exhaust. I suspected the inlet strainer, on the thru hull, was dirty or clogged (as we had just experienced some flooding and rough water from "Sandy", but nothing like our friends, neighbors and loved ones up north). But after removing the hose I found that was not the case. And then I remembered about the engine heat exchanger/exhaust elbow. The water from the heat exchanger passes thru a hose loop before it enters the exhaust elbow.
This image shows the rear of the engine and the arrow points to the location on the exhaust elbow where the water enters from the heat exchanger. You can see the beginning of the hose loop just before the arrow (the up hose), the down hose and the plumbing right angle into the exhaust elbow are removed. The plumbing right angle is shown in this next picture:
It is this right angle and the following entrance into the exhaust elbow which usually gets plugged with small pieces of debris. It is pretty easy to remove (access from the side or back) and to clean out both the plumbing fitting and the elbow entrance with a small piece of wire. Once I did this the water out of the boat exhaust was back to normal.
Knowing this and being able to make it right sure beats a trip to the yard!
Prayers and best wishes to those up north!