I noticed my coolant had leaked all over my driveway, it is coming from the back part of the engine. I was below zero and my engine temp was up over 210 and the heater wasn't blowing hot air.

I refilled the overflow with dexcool and the engine temp returned to normal and the heat was fine, then it must have leaked while driving to work because the heat stopped and the engine temp rose, the coolant overflow was empty again. Any suggestions?

 

Don't know what you mean by "I was below zero".
The first thing I would check is the intake manifold gaskets. With a mechanics mirror and a good light you can try to look at the rear corners of the intake manifold.
Be sure to keep the coolant filled untill you get this fixed to keep from damaging the engine. As a temporary measure you can leave the radiator or coolant tank cap loose. This way it will not build pressure in the cooling system and the coolant will not leak as fast.

 

If you had plain water in the system when the Temps went to zero, maybe you popped a freeze out Plug.

 

Check your oil too, make sure you aren't filling your oil with water too. When my intake gasket leaked, it added water to the oil, and at start-up I could hear a ticking sound ( caused from the sump pulling water up through the oiling system first, then it would quiet down once it was pulling oil ). I started it about 3 times before realizing what was going on. Anyway, if you decide to do the work, go to the dealership & spend the 60 dollars for the all aluminum gasket and get the 20 dollar dealership gray RTV caulking. AND do yourself another favor while you have your heater hoses disconnected, and back flush your heater core with low pressure from a garden hose. BTW, you don't have to separate the upper intake manifold from the lower. I have a couple photos in my photo album, I can add more if you want.

 

Old wives tale about welch (freeze) plugs popping out if water freezes in the cooling system. It is possible for them to pop out when it freezes but more than likely the block will crack anyway. The plugs were not put there for that purpose. They are there to get the sand out of the casting when the block or cylinder heads are cast.

 

I was thinking freeze plug also, esp coming from that part of the motor, Had 92 chevy camaro that had that problem and by the time I got it to the dealer (traded it in) it was pouring water out of the bad freeze plug...Traded that sucker just in time..it was a rear freeze plug and the only way to get to it would be to raise the engine and I wasn't in the mood for that. I pick up one of those new 1995 Ford GTS Mustangs (only made for a couple of years) but made for speed (second childhood thing) and the last yr for the old 302 engine. It would do all of the 150 on the speed-o, but the brakes were poor and I fry the brakes (front) rotors many a time, good thing for that warranty..hahahahahaha..