Volvo Penta Thermostat.
Your thermostat is an intergral part of the cooling system and should be checked regularly for correct operation. Coolant should be changed, preferably with ready mixed, every 2 years and the the heat exchanger removed for cleaning every 5 years.
Volvo Penta Part No: 888624
For Volvo Penta Diesel Engines: D2-75, D2-75B, D2-75C, D2-75F, D2-75A, D2-55C, D2-55D, D2-55E, D2-55F, D2-50F, D2-60F