i have a 98 v-6 blazer. i have flushed out the heater coil and i have replaced the thermostat. i only seem to get warm air out of the vents when the engine is over 2500 rpm, otherwise it is just cold air. any ideas...?

 

Does the engine come up to normal operating temperature (about 1/2 way on the gauge)?

 

the engine actually rarely gets above 1/2 way on the temp. gauge. it seems the engine is being cooled normally.

 

Mine did that too. I bought a cheap flush n fill kit for the radiator and flushed it out. A bottle and a half of 50/50 anti freeze and it's hotter than it's ever been.

 

check your hoses going to the heater core...both should be roughly the same temp when at operating conditions...do you see coolant circulating while it running? Mine just blew cold air until I flushed the heater core directly with a garden hose...outlet to inlet first, then inlet thru outlet..rad cap, thermostat, and water pump are good areas to check as well...dex-cool has done nasty things to many vehicles from what i hear....