oil temp guage always stayed seated at 150 deg. and never moved, today I removed it from the bottom of the oil pan and cleaned it. a little bit of sludgy oil came from the very small oil passage holes located at the base and the tip of the sensor. just cleaned it with brake cleaner and removed debris with compressed air and bingo, works great. these holes are so small it looks like even the smallest particles could plug and cause malfunction.
hopes this helps.

 

Thanks... So I take it you need to drain your oil before doing this right?

 

yes,or just get ready to catch the oil when you pull the sensor, it will come out fast.