Thermostat Differences - Closed Cooling/Raw Water Cooled
 

The top one is a spare I carried in my boat that was raw water cooled , and the bottom one came out of my closed cooled engine in my new boat. Are they interchangeable?
Both are 160 degree.

Closed Cooling Diagram


https://cimg8.ibsrv.net/gimg/www.off...3d4992d264.jpg

https://cimg4.ibsrv.net/gimg/www.off...52278dd1b2.jpg

They are different. The brass looking one has a disc on bottom that closes/opens a passageway. The stainless looking one does not.

Thanks SB. I have seen that disc before and always wondered what it was for. I assumed it was to help the thermostatic spring, like new and improved or something.
I just shined a light in the housing and, yep, there's a passage to open and close.