One problem related to radiator has been reported for the 1998 Subaru Impreza. The most recently reported issues are listed below.
The engine kept overheating and air would appear in the radiator. Antifreeze would be pushed out of radiator and the heater would blow cold air. The car had to be shut off repeatedly and allowed to cool down and the antifreeze replaced. A check of the cooling system detected no leaks. We were took the car to a number of garages until finally one garage told us that the engine block was most likely cracked and the engine needed to be replaced at a cost of $3600. According to the garage, they have replaced a number of engines for this particular model, specifically one with the dohc.