My lexus es 350 engine shut off while driving on hwy w/o prior notification of any error messages. mechanic said diagnostics pointed to cooling system error - water pump related. the pump was repaired. car temp light would fluctuate from cold to hot back to cold. mechanic said cooling system appears to be functioning but sensory gauge still fluctuating. dealer mechanic said water pump needed to replaced but this was already done. then independent mechanic informed me that engine overheated and warped. now car needs engine. car initially shut down on highway w/o warning.