You would have much more siginificant leaks when under load when the system is pressurized. Also you would have water in your oil or vice versa. It has to be a leak in the cooling system somewhere that is running down the side of the head. As a somewhat side note- I always found that coolant pooling by the starter is a sign of overheating, as when it spews, thats where it ends up. Are you using the stock temp gauge or do you have a more accurate aftermarket mechanical one? Things to do- check for water vapor in the exhaust, do a compression check, a leak down if you have the capibilities, tighten all hose clamps, drain your cooling system, park it on a hill and put a hose in the the radiator and try to isolate the issue. I would guess that if you had a cracked water jacket in the head, the issue would much more apparent with a pressurized system. I Doubt the short block water jacket is the issue either. Good luck