Hi Mike,
I had similar happen.... My 12/1 has a 220v fan on the radiator(2 actually)... When I installed the Auto changeover for the output on the alt to overcome the utility, I lost one brush wire on the alt... I didnt notice because the utility power kicked in and powered everything... the fans of course, stopped running, engine was ticking along unloaded for about an hour with no forced draft cooling under minimal load... There actually wasnt much heat generated.... The radiator was hot, too hot to touch comfortably, but certainly not boiling.... Day temp was around 30C if I remember.... The little bit of air wafting about by the flywheels was pretty much enough to stop disaster....
Do a test... let it run, unloaded, for a reasonable time, no fan, and see... You might be surprised....
Cheers
Ed