A couple weeks ago I was flying my C model to the avionics shop to have the IFR check completed.  About 15 minutes into the flight I noticed my oil temp reading was high.  I checked the EGT, CHT, and Oil pressure and all was normal.  I decided to descend and divert just in case.  During the descent the temperature gauge didn't drop a bit to indicate any cooling but all other gauges remained normal.   Once on the ground I figured out the gauge wasn't reading correct and tapped it a few times and