HELP! Why does temperature gauge go up to normal than come down to a little above cold?

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Hey everyone so I was wondering why the temperature gauge on my 1993 Ford Explorer 4.0L 4wd xlt goes to the middle of the gauge aka operating temperature then it goes back down to above cold? I just put a 3rd coolant temperature sending unit it 30 minutes ago because it was fluctuating between hot and normal but everytime I replace the cooling temp sending unit it fixes it thank you.

 

[Centaurious]

Hey everyone so I was wondering why the temperature gauge on my 1993 Ford Explorer 4.0L 4wd xlt goes to the middle of the gauge aka operating temperature then it goes back down to above cold? I just put a 3rd coolant temperature sending unit it 30 minutes ago because it was fluctuating between hot and normal but everytime I replace the cooling temp sending unit it fixes it thank you.

I run a 10 degree hotter than stock thermostat and it stopped the fluctuation. Maybe you have a coolant leak?

 

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I run a 10 degree hotter than stock thermostat and it stopped the fluctuation. Maybe you have a coolant leak?

It's been fixed it turned out to be the coolant temperature sensor again