Help Thermostate missing

[Firstimer]

1987 Sea Ray 17 foot. With a 181 140 hp engine. Boat was over heating so I bought a new thermostat. When I removed the cover to remove the old one all I found was a washer with a small hole in it covering the place where the thermostat should be ....I am lost. Any HELP

 

[Bt Doctur]

called a restrictor plate , used in racing motors to prevent a thermostat failure
or the remains of the original thermostat disintigrated

 

[Firstimer]

Thank You. Next question is should I leave it in or replace it with a thermostat. Boat goes about 35 mph fully open.

 

[Bt Doctur]

A thermostat will help it keep the correct temp