[Hayabusa630]

Disclaimer: I know enough about cars to know that I don't know enough about cars. **Any information or advice re: the car is appreciated immensely**

A brief history as to the relevant car. The car currently has 142K on it. Every thing is updated, checked, etc. on a regular basis (belts, hoses, misc. fluids, etc.). The car has accumulated plenty of miles as of late due to work (23K in the past seven months). V6, 3.3, SE. Last July, while in a traffic jam for about 2-3 hours on a record setting warm day, the car overheated in a big way, huge plume of smoke, etc. After that the water pump, thermostat, an oxygen sensor, and a hose (I believe one of the heater hoses) was replaced. A coolant flush was also done to eliminate debris from the overheating.

From that point on, as long as I did not turn the heat or AC on more than level one on the car, there were no problems (there was an instance in November where the car overheated after the defrost was turned on full blast because the car ran out of antifreeze again).

Last week the car overheated again on a day where it was -4 when I left for work. The car was pretty much out of antifreeze, so I put 3/4 of a gallon in, waited an hour, and it was OK. Today, the car struck back. When I left for work this morning it was -8 (don't know if that is relevant). The car overheated again, I tried the same thing as last week, the car readily guzzled a gallon of antifreeze, and it got me nowhere.

There hasn't been any antifreeze mixing in with the oil, that I am aware of, so that leaves me hoping/thinking I won't have to worry about the intake manifold gasket (with the mileage on the car, such a job would probably mean getting rid of the car). However, antifreeze is not dripping or leaking anywhere at all and over the past two weeks it is disappearing at an insane pace; the antifreeze has to be going somewhere, right? Putting in the gallon this morning did nothing. A mechanic recently recommended a radiator flush earlier this week, but I didn't want to mess with the car in weather like this (if relevant, boy, that paid off, huh?). It seems like whenever the car calls upon a large amount of antifreeze, the antifreeze isn't getting to the radiator, but is going somewhere else, causing the car to overheat (since this is happenening whenever the heat or air are turned up or the weather is particularly awful).

1) What tests could/should be done on the radiator and heating/cooling system to see where the problem is...&...2) What part/s might be the problem this time around (or again). Thank you in advance to those who respond.