I was attending my EAA Chapter meeting Monday which was hosted by Central
Cylinder here in Omaha. They had a couple of Rolls Royce Merlin engines in
the shop, one fully assembled and another partially assembled.

One of the staff there has a lot of time working on Mustangs so I popped off
a couple of questions regarding the cooling system (specifically the cooling
exhaust doors.)

He said that these were set to an automatic mode during takeoff (seeing as
the pilot pretty much has his hands full at that time) but it set to a
manual mode during cruise. The door is adjusted until you get to the right
temperature. After that any change would indicate that a problem exists.

This is the only means of temperature management. No thermostat exists
(which makes sense now that I think about it.)

T Mann