Sudden steam usually means something suddenly let loose - like a coolant hose, or the coolant reservoir, or a plastic side tank on the radiator.
The radiator side tank suddenly split on my 2.7 one time, dumping all the coolant very quickly - and I kept driving (saw the sudden cloud of steam, but assumed that it was because I had driven over a water puddle - wrong!) - temp. gage didn't show overheating because there was no coolant in contact with the sensor. I stopped and looked things over and it wouldn't start. I assumed I had done her in. The good news is that once it cooled down, it started up fine (only thing I can figure is after I turned it off, the heat soak either got to the cam or crank sensor or fuel rail, and no problem once cooled). I replaced the radiator, and it has been fine ever since, as if nothing happened. Still driving it.
So check for a crack in one of the radiator side tanks - usually, but not always a vertical crack up the rear side of the passenger-side tank, and the reservoir - usually cracks on the side facing the engine. If neither of those, check hoses, and the metal pipe on driver's side of transmission that goes downward towards the front, and connects with a 4" long piece of heater hose to the thermostat housing, just behind the alternator - it can rust thru.
'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs