yes, add it in both.
I have proof it works. Logging with DSMlink on my 97 GST Spyer, during 110* cali summertime heat with a large FMIC blocking the radiator my CEL was set to go off (programmed via dsmlink) any water temps over 220*. It would happen alot at stops, because there just wasnt enough air coming into the radiator to help matters, even running both fans full bore at all times didnt do much.
after a can of water wetter temps dropped down to a consistent 205* with the same conditions (Stop and go traffic in 110* heat). I later added a special shroud that poked 2" under the bottom of the car to pull in additional air during cruising, and a shroud between the fmic and radiator, so any air that was going through the fmic had to also go through the radiator. new cap, coolant and more water wetter, and a 170* tstat and temps under same conditions listed above were 195* at a dead stop and 180* during highway cruising speeds. for the remainder of that summer and my terms with the car, the CEL never again went on for coolant reasons. Its a DSM, so the CEL went on for other reasons afterwards.........