Hi WomaninPain,
What you are describing are signs of TMJ. You need to be really careful about the popping. When you open your mouth "too" far, the meniscus (disc) that cushions the TMJ is being stretched or pulled out of position and getting caught. That is why your mouth gets stuck open. The fact that you aren't in pain (except when putting the jaw back in joint) is good. The crunching sound you hear, tho, is a little troubling. That usually is a sign of osteoarthritis (the break-down of cartilage, of which, the disc is mostly made of).
I don't want to scare you. You can live with arthritis and TMJ with no or little difficulties if you treat your jaw properly. That may mean no more gum chewing or eating anything that puts extra stress on the jaw (tough steak, taffy, etc.) Talking less, watching your posture at the computer, being careful not to open your mouth too wide for too long, and being gentle with your jaw and mouth are all helpful. There are also exercises that you can do in an attempt to strength the jaw, but only do them when your jaw is not in stress or pain - check out nismat.org/ptcor/tmj for some basic info and exercises.
I also urge you to see a dentist as Dyan said. If your current dentist is not all that up-to-date with TMJ, seek someone who is.
Please ask any questions you might have here. Educating yourself is so very important. And try not to pop your jaw (relax and ease the disc back in to place).
God bless...
Carol