Zener-protected Power MOSFET Benchtest: Good?

[OpenCircuit]

f3nk80z: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&sqi=2&ved=0ahUKEwjezuHdh_DSAhWh3oMKHR3ODhMQFggaMAA&url=http%3A%2F%2Fwww.st.com%2Fresource%2Fen%2Fdatasheet%2Fstf3nk80z.pdf&usg=AFQjCNEaI3qG2ReJG8W6BrdJMS0PV1gQAw&sig2=nKHdcn20BdDQCsgyQEDH3Q&bvm=bv.150729734,d.amc&cad=rja

Pin 1 Gate
Pin 2 Drain
Pin 3 Source
 
Does this test indicate proper function? When I remove the +5v supply from the gate the fan stops running (when i put 4k resistor across 1 and 3)?

[strawberry]

Gate capacitance(485pF in this case) keeps MOSFET open for a while(if not pulled down). With higher Drain current, Gate will discharge faster by it self and under Gate treshold voltage (of 3.75V in this case) will turn MOSFET off.

STD3NK80Z in datasheet Fig7 show Transfer characteristics show that your Gate voltage(5V) is too low for your setup And MOSFET wont deliver sufficient current to load.