Those match instructions that came with a new heater core for a Ford truck. Measurements < .3 volts are considered ok. Anything over and the coolant needs to be changed. Supposedly electrolysis takes over at .3 volts.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.