I'm actually still having this problem, even though I use a a chunk loader that very easily covers the area of my 4 turtles. Each turtle also has multiple hundreds of thousands of fuel, and a chest to dump in to.
If I leave the area, even just for a moment, I come back to them frozen in place. This same setup used to work, but it suddenly stopped.
Anyone have any idea why? I use the chickenchunks cunkloader (yellow with the floating crystal), and it works fine for the other things I use it for (my base, nether lava pumps).