Mercruiser Thermostat

It is located on the front of the exhaust manifold under the tank. Here is a link to the schema. Scroll down the list until you find your year and engine, and watch the exhaust manifold.

http://www.marinepartsexpress.com/merc_s ...

There are many configurations, but most are at the front of the motor above the water pump on consumption. with pipes coming out.