Engine temperature fluctuates in Dodge Spirit

From 3/4 hot to full cold sounds physically unrealistic, even with an air bubble. I expect it is an electrical problem. The Car Talk guys would say to fix it with black tape (cover the gage). I hope it doesn't have the 2.2L I had in my 82 Aries. Mine got a bad head gasket leak (oil in coolant), which was common in that engine, and one reason you rarely see a K-car on the road today.