you need to insure that your not mixing coolant types and brands as this a factor for early failure. stray current is also a factor and the web has some good reading on test procedures.

I took the opportunity to fit a low fluid alarm when I had my radiator out, there available at flexi drive in Bentley.
unit off the web, other type of sensors are available.

http://www.ebay.com.au/itm/LOW-COOLA...7028%26ps%3D54