For that post I was wearing my engineer hat instead of my doctor hat
Since you seem to know Ohm's law, How long can his 650 CCA trunk mounted battery sustain a 25 amp draw with the engine off @ zero ambient temp before he can't start his car - causing him to miss his Doctors appointment?
Zero degrees and he's overheating so badly he has to shut down but keep the fan going to cool the radiator? Sounds like the worst case scenario. At that point, I'd walk away from the car.
No need to run the fan any longer than 90 seconds with the engine off to fully cool the radiator. I've tested this. From scalding hot radiator to cold to the touch. If the engine is overheating, that's the time to start it up, give it 2500 RPM to add amps back to the battery and circulate the water.
If his battery can't supply power for 90 seconds with the engine off, again, he has other problems.
