If you could look at a cross section of the water distribution manifold, you would see an internal bypass passage that connects the water inlet passage
to the area above the thermostat. When the thermostat is closed, the cold water bypasses up to the tee which feeds the exhaust cooling. When the
thermostat opens, the cold water goes into the engine cooling system before returning past the open thermostat and up to the tee for exhaust cooling.
Again, there is an excellent diagram of the flow paths, with the thermostat open and closed, in the OMC manual.

Jim wrote:

One last question: How do the exhaust manifolds get water if the
thermostat is closed? It looks like it wouldn't come through the
distribution manifold unless the thermostat is designed to leak some.

Jim Kelly wrote:

That is correct, the water distribution manifold takes the place of the thermostat housing used on the automotive version of this engine. I am
NOT referring to, or suggesting that you need to remove, the intake manifold.

In the automotive version, the thermostat fits in a slight counterbore in the top of the intake manifold. The thermostat housing is bolted on
top. In OMC's conversion, a water distribution manifold is substituted for the thermostat housing and a marine thermostat is located in a
counterbore in this housing. The referenced ring fits in a groove after the thermostats is installed. Remove this ring and the thermostat will
come out.

You are also correct in your analysis of the water flow. The water distribution manifold and relocated thermostat are necessary since, unlike an
automotive engine, the exhaust manifolds must be cooled regardless of thermostat state.



Jim wrote:


I had to think about this for a few minutes. So "water distribution
manifold" = "thermostat housing". right? And there is a ring under the
thermostat sitting in the top of the housing that can be pried out to
remove the thermostat?

Jim Kelly wrote:


If it separates after tapping, you have cracked it in two, since it is one piece. The thermostat is secured in the water distribution
manifold with a retaining ring. The thermostat sits up against a ledge or counterbore. The retaining ring then goes in a groove in the
manifold to keep it from dropping down. To remove, turn the manifold upside down and pry the ring out. You will the be able to remove the
thermostat. If you need a diagram, look at page 5-11 of the OMC Cobra manual.

Jim wrote:



"Lawrence James" wrote in message thlink.net...


If it's anything like a merc the housing is two pieces.

That's what I first thought too, but this looks like it's all one
casting. Maybe I need to tap it little to see if it seperates, but it
sure doesn't look like it.