I've done this and Frank is correct, they are difficult to access. I believe I had to pull the front wheels off and use a long extension from inside the fender well, through the rubber splash guards. They may take a bit of torque to crack off depending on the corrosion inside. I would recommend a 1/2" drive. I only did it because I was self doing a major coolant flush, but have since found it easier to pay a shop the $65 for a flush machine coolant change.

92 Montero LS 3.0L V6 Auto, Stock, Original owner, 185,800K miles