The 140-foot-tall coaster will have four inversions and a top speed of 62 mph.
Theme park roundup: Hersheypark closing Wildcat / Low crowds at Lost Island / ‘Nope’ set at Universal
The 1996 coaster will see its last riders on July 31, at least in its current form.
Magic Mountain's 20th coaster will also be the tallest and longest single-rail coaster.
The temporary closure was described as "unscheduled needed repairs" on the coaster trains.
Iron Gwazi will open on Feb. 13 for passholders and March 11 for the general public.
The $13 million coaster will feature multiple inversions, including a new element called a "Raven Truss Dive."
Iron Gwazi will be the world's fastest and steepest hybrid coaster when it opens in 2021.
The 52-mph, 113-foot-tall coaster will be built by Idaho's own Rocky Mountain Construction.