It's better to use a proper thread sealant rather than thread tape, but it sounds like yours is making an earth, so your problem may be somewhere else.

If the gauge is only moving slightly either the thermostat is not working, you have the wrong sender or the gauge is faulty.

The easiest test for the DIY/home mechanic is to disconnect the sender wire & get a 25 ohm resistor (if you car is HJ-WB) & connect the sender to ground thru the 25 ohm resistor. The gauge should read around half scale. If it does, your gauge is OK & you need the correct sender. If it doesn't, your gauge is faulty.

Dr Terry