George, it would have to be drained down to somewhere below the level of the sensor. If you can point the rig uphill, the sensor will be at a higher point and you won't need to drain as much coolant out.

If you're not sure the level's low enough, just be real cautious when you unscrew the sensor; when you get to the last few threads, be ready to put the sensor right back in if you get a lot of coolant 'gushing' out.

If you're REAL fast, you can replace without draining (LOL). Not recommended though!!!! <img src="/forums/images/graemlins/smile.gif" alt="" />

HTH and Happy Draining............ed