Hi grey-hair. Welcome to the forum. Sounds like a problem with the coolant temperature sensor if the radiator fan doesn't turn on without having to turn the AC on. To verify the lack of a fan is causing the overheating, next time it runs too hot, turn the heater on maximum hot and fan on high. That will act like a small radiator.
Also check for multiple fan relays in the fuse box under the hood. Some cars have a low and a high speed relay and some have one for just the radiator fan and another that runs both the radiator and the AC fans. A fast test for relays is to switch two indentical ones around to see if a different circuit stops working.
Some vehicles, minivans in particular, use an electronic fan relay module with multiple inputs. That would also be a likely suspect.
Sunday, July 4th, 2010 AT 2:45 PM