Actually the engine temp warms up fine, it warms up about 10 min. before it's driven but the heater blows cold air until it's driven down the road a few blocks, then it starts blowing warm air and seems to be fine then. It's like the heater core doesn't let hot water through until it's moving awhile.My heater on my 2004 Chevy Impala doesn't work, it seems until I move the car. The blower works, it just doesn't blow hot air. Any ideas?