2021 Mach 1 Break In Complete - First Oil Change Surprises. Today I completed the 1000mi break in of my 2021 Mustang Mach 1 after owning the car for 3wks. Along the way there were some surprises including a bit of oil consumption and a random coolant leak. In this video I cover what to expect during your first 1000 miles, what to keep a close eye on, and what makes the 2021 Mach 1 different from other 2018+ Ford Mustang GTs when it comes to general maintenance.