I have the same problem at 117,000 miles, with a japanese built 2004 RX330. Luckily, no coolant in the oil, no coolant under the oil cap, no coolant in the tranny oil so I hope there is no problem with head gaskets or anything like that. When the heater is on, I get heat when I'm moving, but no heat when I'm idle. I've had to fill the radiator overflow reservoir with coolant a couple of times in the past month. The temp gauge would start to spike high, the radiator fan would also kick in more often. I would pull over and shut off the engine as soon as I see the temp start to spike. I checked the radiator and from the top on both left and right sides and can see signs of orange colored residue running down the sides. Not sure how bad the problem is, but I have an appointment to have it checked out. Any comments? I assume the radiator is shot....