Following is a commonly used method for replacing the heater hose quick disconnect (QD) fittings on many General Motors engines. These fittings can be found on 3.1, 3.4, 5.7, and 6.2 liter engines. Over time they have a tendency to leak and when you try to remove them they usually break off. If your motor has this type of fitting on it you should consider changing it out sooner than later. This will improve your chances of being able to remove it without breaking it. The replacement fitting is a much improved part and is likely to last the lifetime of your vehicle. The following list of tools starts with the bare minimum (first 6) needed for the job followed by the more advanced (and proper) tools you may or may not have in your toolbox. While the job appears a bit daunting at first, it really isn't all that bad and hopefully this tutorial will help you over the rough spots.
BTW, if you think an EZ-Out will get the broken piece out of the manifold, you will likely just end up with a bigger mess.
Tools and Parts
1) Large crescent wrench
2) Fine tooth Hacksaw Blade
3) 1/4" or 3/16ths" Drift punch - modified to a chisel point
5) Needle nose pliers
6) 1/2" - 14 NPT Tap and thread cutting (light) oil
7) Replacement QD Fitting
Electrical tape (optional)
1 1/16ths inch deep Socket and 1/2 Drive Ratchet for R&R of QD Fitting (optional)
T- Bar handle for tap (may not have enough room to use) (optional)
Smaller crescent or 17mm six point or 15mm or 5/8ths twelve point socket for tap when there isn't enough room for T-Bar. (optional)
Assuming you have already tried to remove the old QD fitting and it has broken off, the first step is to make three cuts with your hacksaw blade into the old piece still stuck in the manifold, like below.
You might want to wrap the hacksaw blade with electrical tape, or at least a rag to protect your hands. I found a handy pistol grip keyhole saw at a hardware store with the fine tooth blades. It offers better control and the tapered blade helps cut the metal evenly in this tapered hole.
Take a look at your tap and the new QD fitting to get an idea how deep and the angle you need to cut. Try not to cut into the threads but don't panic if you do mess them up a bit. The tapered tap will clean them up nicely.
After making your cuts use the modified punch and hammer to tap the three pieces away from the manifold threads.
Try to catch the pieces with your needle nose pliers before knocking them completely loose down into the hole. Note that the pliers pictured have very thin jaws allowing you to get down into the hole in case they do fall in. You can always stuff a paper towel down the hole to try and catch the bits beforehand.
Once you have all the pieces out, squirt some cutting oil onto the manifold threads and run the tap in until it starts to get a little tight. Back off the tap a turn then screw it back in again until it gets tight again. You don't want to run the tap all the way through the threads, or even very deep for that matter. Just enough to clean up the threads. Stop and remove the tap after one or two reversals to inspect the threads. Less is better in this case.
After you have the threads cleaned up, wrap the threads of your new QD with Teflon tape making sure not to wrap the first thread and wrapping in the direction that doesn't try to undo itself as you screw the QD in. Or use plumbers pipe sealer.