Back in the early 60s I had a 59 ford with a 406fe in it with an
oil temp sensor in the side of the pan-------when it would get over a quart low the guage reading would drop a lot------meaning
oil probably wasn't reaching the sensor when there was a lot of
oil upstairs------
But-------take out the sensor, get a pan of water and thermomentor--check the ohms as temp rises on the stove and log temps/ohms---------to verify that sensor is correct-----