Engine temperature on my Plus 8 seems to be controlled by both the thermostat and the fan, triggered by the overall engine temperature. It doesn't seem linked to engine revs other than in the winter when the engine revs at 1000 rpm until it is up to about 50C. In the winter the thermostat seems to stay shut until the engine is at about 110C, then the engine temperature drops rapidly to 80C and the cycle starts again. The fan is often running in summer, rarely in winter. I used to worry aboutt this variation, but in the 8 years I've owned the car it has remained the same.
If the engine revs are dropping to the point that it stalls then something is wrong and it needs looking at by a competent technician.
