[Tatsfield]

+1 Don't add antifreeze unless you are 100% sure of what the existing antifreeze is in your cooling system. They used to say not to mix blue and orange but even that is not 100% reliable for all antifreeze types, so best totally drain and flush and refill with new. The only way not to take this risk is to only add water and that substitutes the risk of under protection in cold weather.