Im not sure is this the right place for this topic
Anyway

my 99 ls1 has problem with coolant. Coolant is overflowing because of boiling, but funny thing is temperature stays at exactly the right place [210]

I added again %50 water and %50 dex-cool [orange one] and fulled
then it overflowed again, it doesn't matter wether I drive fast or under 2000rpm
it does this when the engine is hot

I added more purified water and did it again, now I added more coolant it must be around %65 coolant and %35water or something like that. I hope it's gonna be fine but I'm waiting for opinions

 

you might have a weak radiator cap. trade someone and see what happens.

 

maybe dude, I'll try it, but when I stop the engine I can hear the boiling sounds but can't overflow anymore because it's overflowed enough [means I have less liquid than usual now] I mean everythings normal, temperature is normal, fans are on, and also mix is ok too almost exactly 50-50. Plus the coolant that I am using verified by GM. I just can't find any problem, more opinions? I'll change the cap and see

 

Hope you don't have a head gasket leak.