High Oil Temperature Gauge
I had similar issues to others (illogically high oil temps after long drives), and cleaning the underhood grounds (back of head, under fuse box/main battery ground) did not completely fix the problem. Additionally, the status of the A/C compressor didn't matter.
Attached are pictures of the schematics and locations of the grounds;
Perhaps discussed elsewhere in this thread, but I didn't see it. The instrument cluster/temperature gauge references a different ground than the PCM, and the oil temp/level sensor uses one of the PCM grounds.
The PCM uses grounds G140, G141, G142- which are all on the back of the motor, and the oil level/temp sensor also uses G142. The instrument cluster, however uses G200 - which is on the drivers side kick panel
So, in addition to cleaning the grounds on the back of the engine, and the main ground under the fusebox, you should clean the paint off of G200. This fixed the problem for me.
See attached diagrams and schematics.