So ever since I've had the engine rebuilt it's had temp issue.  It runs fine just that after a short while the temp gauge will max out.  I have checked it with an IR thermometer and all of the readings read okay.  Usually around 170 on the rad, 190 on the t-stat housing, 190'ish at the sending unit.  It doesn't matter whether it's on the road or sitting still.  It shouldn't be the IVR since the fuel gauge works fine.

So today I decided to first try replacing the sending unit.  When I removed it I did have some coolant pour out and onto the valley pan.  I installed the sender and wiped up as much of the coolant as I could and then started the engine.  After it had been running for a while, about fifteen minutes, I heard a bang.  The oil cap had blown off the draft tube, the filter in the breather cap had blown out, the dip stick was partially out, and the valve cover gasket on the left head had blown out.  It was, of course, steaming.  Before this had happened I had been measuring the temp and it was only at about 125.  

Has anybody ever seen this happen before?  I assume that it's from the coolant that was spilled even though it was a small amount?