8N coolant capacity is 12 quarts but you knew that by your Essential Manuals. Like Jim said, fill to top of core. Overfilling (and under is #1 overheating issue) and use a thermostat.
THE N-NEWS – WINTER 2020 ISSUE:
BRUCE HAYNES – COOLING ARTICLE:
FORD 8N TRACTOR ESSENTIAL OWNER/OPERATOR/PARTS/SERVICE MANUALS:
Tim *PloughNman* Daley(MI)