Water Pump Fail
Water pumps on JD tractors fail from time to time, which causes the tractor to rapidly overheat.
However, the fact that the tractor gets hot so quickly means it's easy to spot before any damage is done.
It's a simple one to diagnose, as the gauge shoots straight into the red and the overheating warning buzzer goes off.
Water pumps cost about 170 USD and they take roughly three hours to replace.