I have completed my second all grain batch, and had some mash temp issues with both batches. I am using a 10 gal. round igloo cooler for my mash tun, making 10 gal batches. I seem to be having trouble loosing temperature during the mash. Both batches were around 22 lbs of grain, room temp., using 170 degree strike water. Temp falls to about 146-148 after about 30 min. I keep the lid ON most of the time, except when stirring 3-4 times. 1st beer was an APA, missed on style, but still very tasty. Second beer is an Oatmeal Stout, just kegged....but seems to be right on the money so far. Please help.