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: 875795
For Volvo Penta Diesel Engines: MD2002, MD2003 and MD2003T fresh water cooled engines