Just adding onto this thread. I had the same issue with a mechanical Smith
oil temp gauge. Mine plugs into the
oil pan. It takes about 10 minutes to register
oil temp but it tends vary to extremes based on speed wind sppeeds likely cooling the wire. I didn’t know about the “ether” and tube compenentry. Mine might be a pure wire conducting heat and transferring the heat to a coil. I am curious if others have an unstable oil temp guage and I’d love to know if installing a heat shield wrap / tube along the wire would correct this.