Seems it about has to be a thermostat issue. If the hose from housing to circulating pump is just warm it must be getting by thermostat all the time.

Slight off-post question, does your hose extender from t-stat housing to recirculating pump have a bead on both sides? If not there can be a good amount of water pressure there and you DO NOT want that hose to blow off the extender!

really? you dont think the bolt holding the housing is grounding to the manifold?

btw, if you dont like that spacer on the lower water pump hose you can use the hose made for a tall deck (500 bulldog) that is longer.

I have had this problem before. Assuming thermostat is right side up, I found drilling an 1/8 weep hole in the flat part of the thermostat flange always cured the problem. This allows any air pockets out that the piddle pin can’t handle. The second benefit was that temperature swings between an open and closed thermostat were greatly reduced: thermal shock. Look it up.

Yes , in closed cooling systems, but in an open system with this t-stat housing an air pocket ? No way.

The tstat in this housing redirects water. It never stops it anywhere.

Based on pics, that is not his issue since he is using the port on the manifold. On Merc stuff, everything is painted so the bolts don't ground well.

Yes, on an open cooling system. Once the thermostat opens the air escapes, but before it opens air is trapped behind the thermostat = thermostat doesn't open.

This is discussion, not anything else.

Not with the housing in question. Flow is never blocked, it’s refirected.

The housing has a lower and upper section. The upper section is where the water goes to the exhaust manifolds.

The tstat does open to the upper section. It is located up against upper part of housing, not down on intake manifold. Thus it does not stop flow. However, when the tstat is closed, there is still a passage just larger than 1/2” on bravo housing (just less than 1/2” on Alpha) that lets lots of water go to exaust. The rest recirculates with fresh water coming in from sea water pump that much goes to tecirculation pump which it’s feed is on lower cavity of tstat housing.

With tstat closed, with this tstat housing, there is no where for air to be trapped, unless by chance the passage from lower to upper is blocked.