4-Motion Overheating

[gordonm40]

2002 4-motion has overheated once before - diagnosed as faulty thermoswitch, which I understands triggers the fan to kick in. Switch was replaced about 6 weeks ago and all seemed OK.

Now think that switch has gone again but not sure. Symptoms only occur in stop/start traffic. Oil temp gauge starts to shift from 90 degress (which is normal) upwards. Car starts to make weird vibrations (straining engine) felt through the pedals the most. Doesn't sound healthy at all!

Listened out for switch to trigger fan and something is happening but it aint the fan kicking in! So when I'm stationary it looks like the switch is doing soemthing, this something is causing the vibration mentioned earlier.

All fluids in the car are fine.

Faulty switch? Faulty fan? Any suggestions?