After a few heat cycles it will be mixed and the same as in the block.

As preventative maintenance I drain the expansion tank and refill with 50/50 Zerex G48.

In my mind I am simply refreshing the additive package a bit a couple times a year spring & fall. I do about a quart at a time which is about 8% of the capacity. Been doing it for years and the fluid looks like new.

I started doing this after I met a fleet manager who did this on all vehicles in the fleet.t

__________________
1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250, Dec 2024 145,000 miles