04 Nissan Murano Overheating

My 2004 Murano (62,000 miles) has been overheating on and off for about 2 months. The mechanics cannot find the problem and when I take it to them they cannot make it overheat (of course). They have replaced the radiator cap, hoses and thermostat; flushed the system and ran a pressure check. Nothing has helped or revealed the problem. The fans seem to be working. Even the Nissan dealership has no clue. I need HELP!!

We have a 2006 and our car is in the shop getting it’s 4th radiator. They’ve all failed in the same way, small leaks in the aluminum radiator eventually cause overheating. We’ve seen no pools of coolant in the driveway. The dealer has done all the replacements. They claim it’s due to ‘contaminants’ in the coolant (50/50 antifreeze and water according to them) causing electrolysis which erodes the aluminum. The dealer is the only party to have added any coolant to the new radiators. This time they’re ‘flushing the cooling system’ (for 2 days now, can you say waiting for a part?). Either this dealership is really incompetent or Nissan has a radiator problem (it is better than a brake problem :-).