is truck safe to run?

What is your question?

Transmission heater gauge shuts down. Cooling fan comes on. Wrench appears on dash. Truck runs fine. No heating issues. Transmission fluids normal. This is an intermittent problem. In 3O km. it acted this way, but went back to normal twice for a few km. each time.

How long has your 2008 Ford F-350 Super Duty had this problem?

Just since driving it for 5 or 6 km. last evening. So then we returned home.