When I first installed my 408, I was having some doubts about the Evans Coolant I was running with as temps were in the 210* - 220* range. I made some other improvements to the cooling system - the shroud making the biggest difference and I have no cooling concerns whatsoever - pretty steady at 187*.
Lots of good suggestions above - in my experience, it's not the coolant.
Champion 3 row 22" rad, 18" 6 blade clutch fan, 180* Thermostat
