WHILE DRIVING ON I40 NEAR TEXAS/NM STATE LINE, OIL COOLER LINE FAILED RESULTING IN THE HIGHLANDER DUMPING OIL ON THE ROADWAY FOR OVER A MILE BEFORE IT WAS NOTICED. PULLED OFF IMMEDIATELY, SAW OIL POURING OUT FROM BOTTOM PASSENGER SIDE OF ENGINE COVER. EXTERIOR LOWER PASSENGER SIDE AND REAR OF VEHICLE WERE ALSO COVERED IN OIL. NO DASH INDICATOR LIGHTS EVER WARNED OF ISSUE. THIS LEFT US STRANDED ON SIDE OF BUSY INTERSTATE WITH HEAVY SEMI TRAFFIC FOR HOURS WHILE WAITING FOR A TOW TO A SHOP FOR REPAIRS, WHERE WE HAD TO WAIT A DAY FOR THE PART. COMPLETELY UNACCEPTABLE TOYOTA KNEW OF A DEFECTIVE DESIGN THAT COULD LEAD TO ACCIDENTS AND DEATH, AND CHOSE NOT TO ISSUE A RECALL! WILL BE SEEKING LEGAL ACTION.