Here are my notes from 2020:

Coolant service done. Drained out almost 10 quarts. Replaced with 50-50 mix of Zerex GO5, distilled water and added a bottle of Water Wetter. Coolant was very clean.
Suggest maybe going four or five years for the next change. 220,873 miles

I'll try to take a multimeter reading tomorrow.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles