Still researching the question, but I think I get it, from reading this link (complex stuff).
http://www.evanscooling.com/maintenance/
Apparently all coolants "vaporize" at some point when they come in contact with the very hot combustion chamber zones, including Evans. This is a rather constant aspect of an engine cooling process, water turns to "steam" (vaporizes) and is recondensed back into liquid by the radiator. These "pockets of air" are for the most part not a big problem but it is fundamentally why we run a pressurized and/or
antifreeze mixture, to raise the boiling point. When temps start to get to high, the size of the "bubbles" increase, leaving hot spots, that leads to pump cavitation (water pump can't pump air) which complicates the problem (to much heat). It also leads to possible ping or knock, over pressurization of the system and thus expelling coolant out of the system (over flow tank, to the ground, etc.).
Now the good news is that this vaporization is a big factor in removing localized heat. Any of you guys that understand the principles of air conditioning can appreciate the tremendous amount of heat exchanged during a phase change, in this case from a liquid to a gaseous state (BIG energy transfer takes place). Evans, like water, also vaporizes, but to a far lesser degree with much smaller bubbles. Because of it's extreme high boiling point it also recondenses back to a liquid much quicker than water.
I think the
oil is getting hotter because it's not in contact, nearly as much anyway, with the phase change that water goes through. The temperatures are more consistent, no sudden changes, no BIG all at once heat transfer. Thus, the
oil temp and water temp tend to equalize, more consistently.
Once you reach a certain temperature, with water, it becomes increasingly difficult to recondense back into a liguid state. The system would reach a "tipping point" of heat that it could not recover from. She's gonna blow Cap'n! And theres nothing you can do about it. Oh wait, there is, you could run Evans instead of water!
And when and if she does "blow", you can remove the cap easier because the system pressure is WAY lower than any water mix could allow for. I tried that, I actually took off my radiator cap off with the engine temp at a 100 c. Nothing happened, the coolant was clearly circulating, nothing to see here, move along folks, I was quite surprised.
Try that with a water based system and you would be looking at third degree burns!