This video will show you all the steps over on changing out the understand in a 2018 Ford Focus.
Steps
1. Drain coolant
2. Remove passenger side headlight assembly (2 screws)
3. Disconnect the 2 hoses
4. Remove the 3 bolts
5. Remove the old thermostat and gasket
6. Install new thermostat (don't fully tighten the screws until all 3 are lines up and started)
7. Reconnect hoses
8. Refill coolant, crank and let it open to suck coolant in then finish filling (check for leaks)
9. Reinstall headlight
10. Smile, you're done!