The temperature range that this cooling water needs to stay in is, no less than 50°C and no more than 65°C.
The water is pumped from a basic pond pump at a rate of about 400-500mlh.
The specs on the pump(15w=1000l or 40w=2500l) don't appear to be consistent with this earlier statement.
I'm going to get a UNO kit today and start a few projects.
I'm not sure but an adjustable valve could be more expensive & complicated.. my feeling is cheaper and simpler to use a 12V DC bilge pump with a half bridge driver (even an L298N module might work) for PWM control.