Hi all!
I must post the due update.
Thus i didn't pressure check the "new" radiator yet, I installed all the cooling tubing and just started the car.
Seems it builds normal pressure on the cooling tubes, and couldn't see any leaking, nothing in the floor or the plastic bottom cover.
No white smoke from exhaust nor motor cage, not even when revving. Neither slumpy goo on the coolant, oil cap or oil rod. Not smoke column off the oil cap hole, not a big drop of revs at idle. Good signs so far, thanks God.
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After some clicking of a bad lifter without oil, it behaved just fine. I drove it around the block for +20mins and seems fine, just only downside, the dashboard temp indicator was a little hair above the middle line. Probably due to the next very problem:

When car's idling, if I turn on the A/C, fan won't start over. Not after a few minutes either. It cools ok though, so the A/C compressor is working properly (also the heat). It DOESN'T stop, slow down or do anything funky, just works and cools as it should do.

The obnoxious cooling system light is just from the beginning every time I put the key in, so I was afraid problem wasn't of the radiator fan, but of some of the sensors or the FCM (fan control module).
So I hotwired the fan motor from the battery, and started right away at the very moment I energized it.

I didn't had the time to check the 50Amps fuse, maybe tomorrow.
But I'm already looking for a used FCM, seems that mine's another of those fried fan control module cases

Alos didn't check the voltage of the reservoir sensor, nor the FCM, maybe I'm skinning the cat before have hunted it.
I'll update on that therm too whenever possible.

​​​​​BTW!! I also performed a head gasket coolant leak with the small 2ampoule blue chemical tester.
After idling 15 minutes of bubbling in the ampoules, reactive liquid remained blue as a mother f*ing Smurf!!!, so seems no head gasket at all (at least leaking inside the cooling system).
Thanks Mr. Kilmister, you heard my prayers. May you ride free in the sky.

​​​​So, keep in mind fellas, seems that FCM can cause your radiator goes bang bang.
Or better said, running your car in a hot day with a non working radiator fan, thanks to the marvelous reliability of the FCM
Only solace, I know that wasn't entirely my fault, I would haven't let the guy drive it without checking on that warning light if I could've had the choice.

I hope this helps someone at least to clarify some points of the diagnosis of a coolant light.

Red.

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