When the gauge goes to hot, has the engine ever actually overheated where coolant came out? Have you checked to make sure none of the rad hoses are collapsed?
Based on your description, it sounds like the temp sensor is bad. Going from normal to hot or back shouldn't happen all at once.
I looked up the part at a nationally recognized parts store and they are under 50 dollars.
Thursday, June 19th, 2014 AT 9:04 PM