My coolant level in the reserve tank is way below minimum, but I'm not sure what kind of antifreeze is in there (Its green, but since that's just dye I'm wary of just color matching). I need to top it off for now (I'll probably flush the system a couple months later myself, but I just can't spare the time now) but I'm unsure of what to use... I heard mixing different types can be detrimental to the engine.... Any advice?