NOPE! Even if the temp drops to or slightly below freezing for a brief period, you will be safe. It would be best if you can let the block and mani's absorb some of the day time temperature.<br /><br />Remember, the water inside has to give up it's heat b4 it will freeze. It would take a long time for water, in the block, to give up it's heat at 28 degrees. Keeping the cover on at nite will help hold in some of the days heat.Originally posted by simple:<br /> Here in Wisconsin during the day the temperature is about 50 degrees give or take, but during the night it gets about 35-40 give or take. Is this still too cold for water to be left in the engine block?