What could be causing this? It just flips out and goes from 0 to max and all over the place like crazy?

 

Well known problem on many Rangers, the factory oil pressure switches are garbage. Not sure where it's at on the 2.3, but more than likely that's your issue. The oil pressure gauge only tells you there's at least some oil pressure. It doesn't vary, either you have no oil pressure and the gauge is at the bottom, or you have at least a couple pounds of oil pressure and the gauge is in the middle. It's really a worthless display and a sorry excuse for a "gauge".

 

Change the oil pressure switch/sender on the engine

Location here: https://www.ranger-forums.com/dohc-2...nd-unit-53660/