On some Thermostats that have the small vent hole, they also have a rivet or some sort of metal 'widget' in the hole. Why? Why put the hole there then partly block it? Also, I've noticed if I drill even just one small vent hole, say 3/32" in a thermostat in a Chevy, when it's really cold, 10deg or less, the engine seems to take a lot longer to warm up than when there is no vent hole. Anybody else notice that?