If it looks good to the exchanger it could be the flow from the exchanger to the exhaust elbow
. When was the last time you changed your zincs? Sometimes the zincs decay and drop pieces. In my case these pieces "conveniently" got logged in the fitting that connects the cooling water
hose from the heat exchanger
to the mixing elbow. It was only after I sourced, purchased and installed a new elbow that I discovered all I needed was a $5 90 or perhaps just ramming a coat hanger into it to clear the part. DOH!
My suggested and admittedly untried test would be to open the cooling
seacock and remove the cooling water hose from the mixing elbow. With the throttle off, crank the engine
and see if you get water out the cooling system.