No heat IN A 2000 GRAND CARAVAN--3.8--PASS. ZONE TEMP. REAR HEAT. PROGRAMMABLE CONTROL PANEL. FLUSHED CORE-DIDN'T HELP. REPLACED CORE AND GAINED 20 DEG. ENGINE HEAT AT 200 DEG. CORE IN 150 DEG. OUT 150 DEG. REPROGRAMMED CONTROL PANEL. CORE IN 160 DEG--OUT 160 DEG. REPLACED ZONE ACTUATOR AT DRIVERS SIDE AND WATCHED BOTH ACTUATORS WORKING AS I SLID BOTH TEMP BUTTONS SEVERAL TIMES. DOOR IS WORKING GOOD. HAD 170 DEG. IN THE SHOP AND WHEN I DROVE IT, IT COOLED DOWN TO 90 DEG. WATER LEVEL IS GOOD AND NO AIR POCKETS. THIS HAS BEEN GOING ON FOR THREE DAYS. ANY IDEAS?
Okay. If it worked in the shop and then cooled down after driving, did the engine temp cool down too? It sounds like you have the HVAC system doing what it should, but maybe the thermostat is sticking causing the coolant temp to drop.