I've been having an intermittent "running warm" condition for a few weeks too that I think I finally figured out today. I've also been smelling antifreeze really faintly too, but could not for the life of me figure out where it was coming from.

I changed the pressure cap and the tstat which were both needed and both helped, but every once in a while it would still shoot up to the point where I was worried...

Well today when I got home I finally saw some steam coming from the radiator and found a spot where some antifreeze was bubbling out pretty good. Verdict: cracked radiator. I think what it was doing is every once in a while it would let in a bubble that would take a while to work out. I'd run hot until it flushed itself out and then it would be fine.

I went ahead and changed the radiator to a new one and did the water pump while I was in there as I have no idea how long it's been on there.

I think it's fixed but of course I won't know for sure until tomorrow.