On Tuesday, April 27, 2021 at 2:18:36 PM UTC-4, TimR wrote:
Also could be a head gasket. There doesn't need to be a leak to let coolant out, if there's a path for exhaust gas to get into the coolant system. Coolant is scared of exhaust and it will quickly flee out of the reservoir or anywhere else it can find.

Yep, this has happened to me.
Had combustion test all is good. Did thermostat and fan clutch. Back to good. 60,155 miles now for sale. Looking for 7. Will accept 8.