The Genuine Yamaha Marine Outboard Thermostat Gasket is a working seal between the thermostat housing and the engine.
Yamaha
Yamaha - Thermostat Cover Gasket - 63P-12414-00-00 - F150 LF150
$7.01$7.85Unit price /Unavailable
Yamaha
$8.45$9.25Unit price /Unavailable
Yamaha
Yamaha - Cylinder Crankcase Thermostat Cover Gasket - 688-12414-A1-00 - 115 130 150 175 200 225
$4.77$5.30Unit price /Unavailable-
Yamaha
$4.91$5.45Unit price /Unavailable 
Yamaha
Yamaha - Thermostat Gasket - 6G8-12414-A0-00 - F6 F8 T8 F9.9 FT9.9 T9.9
$6.79$7.55Unit price /Unavailable
Yamaha
Yamaha - Thermostat Cover Gasket - 60V-12414-A0-00 - LZ250 LZ300 VZ200 VZ225 VZ250 VZ300 Z450 Z300
$3.68$4.15Unit price /Unavailable
Yamaha
Yamaha - Thermostat Gasket - 67D-12414-A0-00 - F2.5 F4 F4A F6A
$5.13$5.70Unit price /Unavailable
Yamaha
Yamaha - Thermostat Gasket - 655-12414-A1-00 - C25 CV25 C30 CV30
$4.84$5.40Unit price /Unavailable
A Genuine Yamaha Marine Outboard Thermostat Gasket goes in the thermostat housing on the lower intake directly to the left of the distributor. There's 2 bolts holding on the housing where the upper radiator tube goes into the lower intake. Remove the two bolts and the housing, and your t-stat will be right there. Most Genuine Yamaha Marine Outboard Thermostat Gaskets are made from high-grade rubbers. These rubbers have several types such as: Silicone rubber. High nitrile rubber.
