1999 "EE" Evinrude 200, 225 V6 FFI Outboards Service Manual, P/N 787025, Page 177Get this manual
Thermostat Servicing Disassembly
1Remove the thermostat coverInspect its O-ring and replace if damaged 2Remove thermostat assembly
3Inspect the thermostat seal on thermostat flange Replace if necessary4Inspect the components for cracks, heat damage, or signs of corrosionReplace if necessary