YUP!
Thanks Steve - I couldn't get a good look but I wanted to be sure that separating the two systems would not require re-routing the cabin heat hoses.
To summarize - I feel that more engine coolant is getting into the overflow tank then just during extreme overheat conditions (radiator belching) and possibly exchanging heat.
I like the idea of isolating the two systems by adding a small radiator tank and then utilizing the stock tank for the IC, but from what you've discovered I would not want to re-route the HE coolant lines to "flow" thru the tank (if the tank has baffles/sections)
Adding a larger, remote mounted tank is the best upgrade for the racers and extreme performance, but for cost effectiveness, adding the small radiator tank will allow me to upgrade in phases.
1. Add small overflow tank for radiator to isolate both systems (under $75)
2. Upgrade to a larger HE ($450)
3. Upgrade to the Johnson Marine Pump ($100)
4. (if needed) replace the stock IC tank with an aftermarket aluminum "flow thru" type tank in the same location or remote.
I wonder if there is a more effective cooling fluid mixture that can be used for the HE that you might not use for a engine coolant?