Purchased a 2005 dakota SLT 4.7L Magnum with 78k on it in jan. after a couple weeks there was a knocking in the motor which the dealer said was a stuck lifter that did no other damage, they fixed it. After that I noticed a significant coolant loss but no spots in the driveway. They said it was the water pump and changed it but still the same coolant loss. Brought it back and they did a compression test, o2 test, pressure test, checked for leaks, freeze plug, and replaced some hoses and the radiator cap. There was no signs of coolant in the oil and some milky residue under the fill cap that I wiped off a month ago and it hasn't been back. No one can find the problem. They then put die in the cooling system so they could find the leak with a uv light they then drove it 200 miles and gave it back saying the level hadn't gone down and marked it for me. After 200 miles I checked it and it was down 3 inches. I did notice a little coolant in the snow after an hour long drive but am not sure if it was from me or another car. I again brought it back after racking up some more miles to try and bring it in while leaking. We both looked under it and everything was dry and the level was back up but still an inch lower than the original line. What are some other things this can be? It doesn't seem normal for the res to fluctuate that much between warm and cold. Should I take it to another shop to try some other tests?