temperature gauge rises and losing coolant rover 45

Hello all my temp gauge rises after about 3 miles of driving then it drops down and repeats this over and over but the thing that has lost me the most is I only lose coolant when the temp gauge rises. But I did notice the other day the coolant pipe at the top of the radiator had no water in there then about 7 miles later it did does this mean I have a problem with my thomostat and if so is it OK just to remove the valve from inside the housing. Also dose anyone have any idea where the coolant is going?

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