Why does Mercedes use Renault engines?
Mercedes does not use Renault engines in their Formula One team. Mercedes has their own power unit division, Mercedes-AMG High Performance Powertrains, which designs and manufactures their own engines and hybrid systems for their Formula One team, as well as for their customer teams such as Williams and Racing Point (now Aston Martin).
However, in the past, Renault supplied engines to the Mercedes works team (previously known as Brawn GP) during the 2009 season when they won the Drivers' and Constructors' Championships. Additionally, Renault currently supplies engines to several other teams on the grid, including their own team, Alpine, as well as McLaren and Red Bull Racing.