over heating what can tis cause?

ok my car started overheating really bad like to the point where there was coolant dumping out of my engine. i replaced all the coolant and i let it idle for a while and its still runs kinda hot. took it down the block a little ways and whener i would gas a little bit the temp would go down a little. also the aux. fan is not turning on what do i need to do to turn it on? what things should i check to see if they are damaged or not?

If your engine overheats only at idle and low speeds but runs at normal temperature above ~30mph, something's wrong with one or both of your fans and they're not pulling in enough air.
You said that your auxiliary fan doesn't come on when the engine's hot. Does it come on when you switch on the A/C? If it does, that means the coolant temp. sensor in the t'stat housing (lower part of radiator in Renix 4.0) isn't working. If it doesn't come on when you switch on the A/C either, that means there's either a faulty relay or a fault in the wiring from relay to fan.
Try jumping the positive power feed of the fan to the battery to see if that makes the fan work. If it does, at least you'll know the fan itself isn't at fault.
You'll also need to check the mechanical fan. Since it's attached to a viscous clutch that stiffens up when the engine's hot, try spinning it by hand (preferably with the engine off ) and see how much resistance there is.

could also be a water pump. Not flowing enough coolant at idle

only time I've ever had coolant actually boiling out of the motor was when a water pump went bad.

Try the waterpump, that was one of my dilemma's last summer. The impeller fell right off inside the block and it had the same symptoms.

Check to see that the wires to the fan are plugged in. Guess what didn't get plugged back in on mine when I had the H2O pump done?