I drained the system, filled it with water and CLR, ran for 1/2 hr, drained again, filled with water and baking soda, ran for 1/2 hr, drained and filled with coolant.
Still no difference. Then I changed the cap from 4 lbs to zero pressure and it seems to be a little better. It doesn't seem to get any hotter than 190.
But still I don't see why it would fluctuate between 180 and 190. I wonder if a bunch of crud got flushed into the rad with the rebuilt engine? Maybe I'll remove the rad and have it flushed.
