Ford-Lehman - what is this part?

OK, firstly this turbocharged FL is in Texas, and the boat it is in is being worked on by a friend of mine for a friend of his to get it ready for sale. The engine is taking a long time to begin showing heat on the gauge compared to its twin and then just keeps right on going until it is overheating. My friend is an experienced mechanic on much bigger engines on charter boats, but he is NOT experienced on FLs. He is looking into all the normal causes of overheating, but we are both wondering what this piece of equipment with three hoses On the coolant, NOT saltwater side is. That's the heat exchanger it is attached to.
The upper hose runs off the the turbo,and the smallest hose probably is going to the shaft packing. The hose on the left comes from the coolant reservoir.

Don't know FL well, but looks like a thermostat housing.

Makes sense, but surely somebody with direct knowledge will pop along here in a minute. He doesn't want to pull it apart without knowing. I suggested, and he may well call American Diesel.

And the winner is.... Lepke as confirmed by the boys in Kilmarnock. It's a thermostat housing. Thanks.

It’s a big old thermostat!

Pop test it in boiling water.

American Diesel has the gasket.

Just saw this thread, I have those on my SP225s. It is indeed the thermostat housing.

hytedin said:

It’s a big old thermostat!

Pop test it in boiling water.

American Diesel has the gasket.

Click to expand...

He already did. New stat on order.

Comodave said:

Just saw this thread, I have those on my SP225s. It is indeed the thermostat housing.

Click to expand...

Is that the primary or a second thermo, just curious

Primary.