One problem related to radiator has been reported for the 1999 Hyundai Elantra. The most recently reported issues are listed below.
2/4/2000 - heater fan & motor assembly replaced (and again on 8/25/2001); 10/12/2000 - radiator appears to blow up, technical advisor "joe stroud" accused consumer of tampering with it to disable it - radiator and thermostat replaced & rear hub bolt assembly; 11/07/2000 - misfire detected in spark plug assembly; 12/30/2000 - battery died in 17 degree temp, car towed to dealership & was refused, towed again after addt'l contact with roadside assistance company (battery replaced file #565541 & Hyundai compensated for rental); 3/20/2001 - temp guage registers "hot" a/c not cooling properly - fan relay replaced; 8/25/2001 - fan motor rattles and temp guage registers "hot" and a/c inoperable - replaced fan motor again (1st repl 2/4/2000); 9/14/2001 - "check engine" light on, no loss of power; spark plug cable set replaced under warranty.