dont mix types, brands, even different versions within the same brand, if you cant be sure what will happen its not worth it, at best nothing, at worse youll bore a hole straight through the block from acid erosion and electrolysis
if you are only topping up the overflow distilled water will be fine, if you need more its a good idea to drain and flush using a proper raditaot flush and fill up with some very high quality inhibitor
We dont need anti freeze, anti boil is useful but not a big concern, however we have an alloy radiator, alloy head, alloy block, alloy water housings and the blocks are already prone to breaking through and leaking coolant so nothing but top shelf for me, I use Tectaloy XP7 organic stuff on recommendation from Richard of A.R.E fame, I reckon he knows about this stuff
