Those holes are to allow coolant to circulate when the thermostat is closed, I think I drill two 1/8 holes in my thermostats also for that very same reason, let the air out so I can fill the cooling system up completely without having to wait for the thermostst to open and it lets a small amount of coolant to circulate while warming up

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)