for testing purposes you should not have added the water wetter. We wanted you find the problem; not fix the symptoms. That way the rest of us don't Fawk it up when its our turn hehehehe. :p :p
For the sake if testing a hypothosis of why it was getting hotter the way to go woulda beeen somedin like this.
. First see of the burping and heat on Hi for a few weeks to finish burp changes things
. then change % of coolant
Course then again if all you want to do is drop your temps back down........ you do what u just did
hope it works out well.