It isn't actually your overflow tank it's the surge tank, if you put it in there as it 's pressurized it will get into the system as you drive. You are much better off fixing the actual problem than putting that stuff into your cooling system
read the guide guide below, it may help
https://www.2carpros.com/articles/car-is-leaking-coolant
The diagram below shows the surge tank
Image (Click to make bigger)
Tuesday, March 2nd, 2021 AT 9:10 AM