i've seen thermostats engineered with a hole and a brass 1-way type valve in it. it's supposed to help purge air when filling a dry system, i think.... or maybe it's to get the heater working faster. i think it measures about .030". not sure of any help or hinderence on the Pontiac8 though. i pretty much see it only on foreign 4s i think. --------------------------------------------------
it sounds like probably an airflow problem if it cools down when you get going. can you feel it pulling air?
