Replaced the radiator cap, and still the system won't hold pressure, and discharges coolant after a 5-mile drive (this time to NAPA autoparts), thus making the coolant level light come on, but again, no overheating.

Luckily, I had placed in some coolant U/V dye and it looks like the rear hose from passenger-side block to heater-diverter valve (124.830.54.96) or the metal elbow that bolts to the block and gives it a nipple is defective.

Waiting for the car to cool before removing the hose to find out . . .

:-( neil

PS: the dye don't lie . . .