I have a 10 gal igloo water cooler (the yellow kind with red lid). I preheat it for 20 min with water well above my mash temp + grain. Every time I mash in a 5 gallon batch I end up about 1-2 degrees above my mash temp. After a 60 min mash I lose on average 4 degrees. I also use 1 1/2" of foam sheeting cut to fit into the cooler to minimize head space to under 6". Is there anything else I can do to hold temps better? The only thing I can think of is I need to add my grain stir, let it sit 10 min then sitr again and recheck my temp incase I am loosing temp in the first 10 min as the grain sucks up some extra heat I dont account for in the first min the grain has been added and stirred.