International DuraStar

The International DuraStar line, known as the 4000 series prior to 2008, is a line of medium-duty trucks produced by Navistar International from 2001 until 2018. Introduced as the successor to the International 4000 series of 1989–2001, the 4000 series was renamed the DuraStar in 2008. Developed as a Class 6-7 product range, the 4000/DuraStar was slotted below the 8000/TranStar regional-haul semitractor, with the Class 5 International TerraStar (2010–2015) serving as the smallest International conventional-cab product range.

The most distinctive features of the DuraStar are the "crescent shape" headlights and a distinctive "black spot" on the left side of the cab. Produced as both a semitractor and a straight/rigid truck, the 4000/DuraStar has been used in a wide variety of applications, including emergency vehicles, towing, flatbed trucks, and cargo box trucks. For bus use, the chassis is used in both cowled-chassis and cutaway-cab configurations for school bus and commercial applications.

The DuraStar was replaced by the International MV Series in 2018.

Blue Diamond Truck alliance

In early 2001, Navistar entered into a 50/50 joint venture to produce commercial vehicles with Ford Motor Company, officially named Blue Diamond Truck, LLC. Under the agreement, Navistar assembled medium-duty trucks for both companies in its facility in General Escobedo, Mexico.

Though externally different, both Ford and Navistar model lines would share a common chassis; the medium-duty Ford F-Series (which had already entered production in 2000 at General Escobedo) shared its cab with the F-Series Super Duty line (F-250 through F-550). Though smaller F-Series vehicles used Navistar-supplied diesel engines, medium-duty Fords used engines supplied by Cummins and Caterpillar.