I would check the thermostat in a pan of water. Have had many a new thermostat not perform correctly. Putting it in hot water also cycles it which tends to loosen them up a little. Also you may need to bleed the air out. Sometimes takes several trips to get rid of all the air.

__________________
Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel