Maximize Fluid Life, Part 3:
Contamination of thermal fluid systems is always self-inflicted. It happens when a fluid with poor thermal stability (hydraulic fluid and glycol solutions are prime suspects since they are often stored in drums in the same area) is added by mistake.
An immediate result may be pump cavitation, or a “geyser” from the expansion tank vent. However, many times the only indication that contamination has occurred is a rapid plugging of the pump suction strainer with carbon generated by the contaminant. Preventing contamination comes down to a simple matter of good housekeeping around the heater.
Have a hose and pump dedicated to transferring thermal fluids. Padlock them to the heater if necessary to make sure they don’t get used for anything else.
Promptly remove any empty drums from the room. You might be surprised at what gets put into them (and then again maybe not).
Don’t store other drummed material anywhere close to the heater. You don’t want anybody who might be illiterate and color blind to make a mistake.
Never ever put fluid from the overflow tank back into the system. It’s in the overflow tank for a reason.