Custom mechanical fan builder

No. best description was it had the consistency of wet laundry detergent. very small chunks of this stuff - white in color, pinched ion between fingers it would disintegrate into tiny granuals. I asked the motor builder if this was caustic soda coming form the motor, and he confirmed that they use a jet washer with no media or soda. No idea where it came from or what it is, but pretty sure it had to come from the motor somehow.

Might be calcium deposits.

Have you done a simple voltmeter electrolysis test? Should be under .3 volts. Connect one side of voltmeter to body ground and dangle other in coolant.

Also check engine ground straps.

Do you mix tap water with coolant or water pump lube in radiator?