Have you tried pulling the thermostat out completely and see what it does? If its not the sending unit, waterpump, clogged radiator/heater core, clogged hoses or radiator cap. It only leaves the thermostat. I usually switch thermostats in F-Bodys (Camaros, Trans Ams, Fire Birds, ect.). I use a 160 degree thermostat. The 305's and 350's have alway given me better results with the lower temp thermostat.
But first and foremost. We need to find out if it is the thermostat. So I'd suggest pulling out the thermostat and run some tests from there. Hit me back and let me know.
Monday, November 3rd, 2008 AT 12:25 PM