Mixing Anti Freeze

[Macski]

Thermostat broke on my car, was stuck open, garage could not do for a few days so did it myself, bought some anti freeze to top up the coolant put a liter in of pretty red anti freeze and thought I should not have mixed it, there again I had no idea what was in it already.

Do I need to flush it now?

[GreenV8S]

You need to find what type was in it previously, find what type you added, look up whether they are compatible. Not trying to be unhelpful, but really it's impossible for us to guess.

[Penelope Stopit]

Yes you need to drain the cooling system and fill it with the correct mix/ratio of water and antifreeze that suit the weather conditions of your country
Unfortunately there is no other solution, excuse the pun