I've recommended that he try a 180° thermostat. Don't know if he will do it.

Interesting idea that it might be an erroneous reading. He has a Scangauge so he can check the temp when stone cold.

 

I hate it that in so many threads the OP doesn't close out the discussion by telling how the problem was resolved, so here's a little good news.

He bought a new expansion tank cap and it appears to have done the trick. It's been a couple weeks now and all is well. Thanks to MC04DII for that suggestion.

The surprising thing about that is that swapping in the cap from my truck didn't solve the problem. Seems that maybe I should replace mine too as a preventive measure.