How can I test it to see if it is the sending unit for the temp gauge or the gauge itself?
You can test the sending unit the same way you test any other car with a temperature gauge.
Just remove the single wire that comes from the sending unit and ground it against the block (make sure you turn the key to “on” position).
If the temp gauge goes all the way past hot, then the gauge is fine the sending unit sounds like it is bad. If you do this and the gauge barely moves, then the gauge itself is the problem.
In most cases the sending unit IS the problem, not the gauge!
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