The answer is, the act of pouring the water over your grains will lower the temperature of the sparge water slightly. The goal of the sparge water is to rinse out any residual malt sugars from your grains. Personally, I don't have a problem with using 170F degree sparge water but some people go a little hotter. It's based on experience, your technique and your equipment as to which answer is right for your needs.
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