Twin thermostat waterpump

[ro_kru]

I am going through some literature of Rolls-Royce diesel engines and wondering how is the working of twin thermostat water pump? Why there are two outlets to radiator? Most of the time I dealt with water pump which has single thermostat in housing.

 

[TugboatEng]

Larger engines use thermostat modules. A housing can incorporate as many modules as required to achieve an acceptable velocity at the required flow rate. Our Caterpillar 3500 series engines use 4 modules in the t-stat housing.

Caltherm is a leading producer of the modules.

http://caltherm.herodev.com/thermostatic-solutions/heavy-duty.php