when I say whiteline (barely op. temp.) I mean the first solid white line. In my worthless opinion, I think your thermostat isn't opening up all the way, thereby keeping the hottest water at the temp sensor, and not letting it cerculate(bah!sp.) to the fan switch thermo probe, if that's possible/makes sense. The other thermo probe is looking sumpin like this
I changed all the parts I mentioned and put the luby stuff in and now I can keep my bra on and she still doesn't get too bent out of shape when I go up the "Grapevine" (a rather largish hill in California). She used to scream "I'm too G.D. HOOOOT!" 1/4 of the way up.
Good luck with that, Z-man and if you figure it out, give us a post, eh?