1987 FJ60, 211k miles with original radiator, in Colorado. Has had some minor troubles over-heating on long climbs. SO, I go slow (is there any other way?). But, this morning, I'm almost convinced that it only will overheat when the heater is on 'hot'. Does that make sense? Usually, you'd turn the heater full blast, so you can dissipate a little more of the heat. . . . Does this mean I may have a bubble somewhere in the water cooling system? Anybody else had this problem?