I bought a 2000 v6 mustang. On the test drive, no issues. However, on the way home, i noticed the vehicle was running to hot. I pulled over about 6 times to cool down. I knew better then to redline the motor. Once i had the money, i bought an entire cooling system and installed it. Except for the heater core, its still the stock one. I noticed last summer, when i was driving about 60 and the AC on, the selected vents changed from the dash to the floor and windshield vents on its own. The air sounded to be more forceful and get higher as i increased my speed. This happened for a few miles and went back to normal on its own. Ive since replaced the AC pump with clutch, accumulator/dryer and the high pressure hose. A autozone AC replacement kit. Now that its getting colder, i need to use the heater. After my vehicle is at operating temp, if i turn my heater on to the floor, the heater work for about a minute before going to cool air. If i turn on the heater dash vents, it blows warm air for about 30 seconds before going cool. Ive heard actuator door, blower motor, vacuum leak and heater core. I dont have tons of money so i cant just replace everything. I also tried to back flush the heater core with a garden hose. I didn't do the best job though. I noticed rusty water came out of the heater hose. I did not back flush the heater core the time i replaced the cooling system. I was a few months after the radiator, water pump and thermostat install. I only back flushed the heater core because I was thinking maybe it was clogged and that's why it blows hot when first turned on then gets cool shortly after. Maybe clogged heater core.. yes, i run the proper antifreeze so i was a bit shocked to see rust come out of the heater core when i back flushed it. Thanks

 

Could just be some trapped air in the system. Might try burping the coolant system. Easiest is simply fill the radiator and overflow full and leave cap off. Start the engine and let it run with the heater on high for about 10 min or so.

 

I have one of those funnels where you attach it to the radiator. I honestly dont think its an air pocket. I'm trying to avoid pulling the dash apart. Thanks daehawk. I appreciate your reply

 

It's rare to have air pockets left behind on 3.8L V6 models, because those engines actually have a little air bleeder on top of the thermostat housing. Makes things so much easier. I can't tell you how many times I've wished that my V8 had something like that.

 

That burp valve does come in handy to purge the air if you dont have one of those funnels