Mixing same color coolant is acceptable?

[Gaurav]

I know mixing red and green color radiator coolant is totally unacceptable, but can we mix different brands of same color - green coolant while top up?

I have filled originally with Mitsubishi coolant and then used ENOC green coolant occasionally to top up since last 1 year. Recently added Prestone green coolant to top up and now I had 3 leaks in 3 weeks. So doubting if coolant mixing could be the cause or is it a pure coincidence.

[treks]

It can happen that the various corrosion inhibitors in different brands of coolant  react with each other to form an acid that attacks seals and/or mating surfaces under gaskets and seals. Other times, and depending on the mixture, coolant additives can cancel each other out, so you may think that your engine is protected, but meanwhile, the coolant mixture is destroying it from within in various ways, and the first time you notice something is wrong is when you start getting coolant leaks. 

So no, mixing coolants is never a good idea. 

[Barry]

There’s also an issue that different coolants will gel rather than mixing which can create hotspots in the engine and cause things to warp or weaken. 

[desertdude]

That's a big no no in the BMW world too not to mix it's blue coolant with any other because it will turn into a gel.

[shadow79]

That's why I ask people to put ac water if in doubt or can't find the exact brand of coolant . As that will only dilute it and not make much issue...