Do you see flaky insulation on harness , specially near the blu temp sensor ??

When you get to 105c . pull the connector off the blu sensor and see if high fan defaults ON.
If so, get a 1K resistor from Radio Shack and put it across the unplugged connector and see if that turns the default fan back OFF.
If it meets these two criteria, then change the sensor.
If not , you have a wiring problem or a sticking relay.
When engine is cold, before you turn the key on, pull the connector off blu sensor and take an ohm reading across the sensor and post the results..

__________________
A Dalton