First, I would flush the cooling system, then add some fresh coolant/water. You can also pick up a bottle of RedLine Water Wetter which might help a bit. Other than replacing the radiator, which it might be time to do, you could possibly wire your fan to stay on and provide some more cooling. Of course, with 137k on it, your water pump could be on its way out if it wasn't replaced at your 90k timing belt interval.