Originally Posted by Baja Rooster (Post 4648483)

Originally Posted by SB (Post 4600931)

1 large in/ 1 large to recirc pump, 1 x 2 outs to exhaust ports

Think of the Tstat housing in 2 halfs.

Water enters the lower and goes to recirculating pump. When the lower half fills it then is able to enter the upper half thru a 'bypass' opening. The upper half is what has the 2 outlets to the exhaust manifolds. This way, the water entering from the sea water pump is prioritized to the recirculating pump. Again, The excess goes up thru the bypass opening into second half which send it to the exhaust.

The t-stat rests/seals against upper 2nd half. Directly over , but not on, the t-stat opening in the intake manifold. When the t-stat is closed a lot of this water get's redirected with incoming water towards the recirculating pump. When the t-stat opens, the hot ater coming from the intake manifold has a straight shot to upper t-stat housing half which goes right out into the exhaust manifolds.

The 4 port Mercruiser t-stat housing is actually, in my mind a stroke of genius. It does not impeded water flow, let's the thermostat do it's ob quite well,and it actually directs water to where it needs to be prioritized. all while letting lots of water thru to the exhaust and out the boat.