I did a quick search for info about testing MB coolant for effectiveness but didn't come up with anything. I have '97 E320 that had its cooling system flushed and refilled with the proper solution of MB coolant about 30 months ago. This morning when car was at dealer for some suspension work, the tech did the usual "courtesy inspection" and announced that my coolant had no freezing protection. Car runs great and temp never goes above about 90 degrees on the guage regardles of outside temp, use of A/c or length of time engine has been run. I want to test the contents of the radiator myself but all that I have is Prestone bulb-type tester that is several years old. Will this tester give a reasonably accurate indication of the properties of the MB coolant solution?

TIA