cooling questions

[bitsilly]

Believe it or not, I couldn't get to the bottom of cooling and am pulling my hair out.
This is what I think I know!

When the block water gets too hot, the thermostat opens a port in the manifold and water flows out, through the rad and back to the pump.

Q1 Do I need to have a valve on the heater circuit which also leaves the manifold and returns to the pump to tune/balance flows or to block a path of least resistance?

The thermostat for the fan can be adjustable or set. My one has 85-75 written on it. Which I guess means it switches the fan on at 85 and off again at 75.

Q2 Should I get an adjustable one as 75 seems low operating temp?

Q3 The SD1 rad has a thermostat housing in the top of the rad, is this a suitable place for the 85-75 fan thermostat or does it need to be in the top hose?

Thats all I can handle for now, my head is tired!

[bitsilly]

Some sources refer to a bypass hose to allow some water to bypass the thermostat. The heater circuit would do this. Don't know why or what for mind!