Well, since I can’t work on my stuff right now due to covid recovery, at least I can get some planning out of the way.

I will be running Merc big block heat exchangers on my 509s and I’m trying to figure out some of the plumbing.

The raw water incoming and outgoing is easy.

There is a connecting hose (in diagrams) that goes from the top tank to the hose connection that returns to the circulation pump. I’m assuming that’s used for surge. That too is easy.

The connection that has me scratching my head is another on the return for the circulation pump that comes from the thermostat housing. The Merc diagram shows a smaller hose coming from the thermostat housing to this connection. I’m assuming that it’s used as a bypass when the thermostat is closed.

What’s the best way of dealing with this connection? I don’t want to use the Merc thermostat housing. it’s complicated and expensive. Diagrams show the intake to the circulation pump bypass still being in place. My Merlin intakes do not have bypass hose connections though they should be easy to fit if I needed them. I was planning on blocking the circulation pump bypass connection and putting holes in the thermostat to move water before opening.

Any thoughts on how to deal with the extra connection?

Any of you that have added one of these outside of being stock Merc want to chime in?