well... 10 degrees above IF you were doing BIAB in your kettle. you want the water temp in your cooler to be about 10 above your desired strike temp when adding those 60-65 degree grains. since the cooler isn't preheated you're going to lose temp to the thermal mass of the cooler coming up to temp.
if you have a large enough kettle, I would suggest skipping the cooler. just wrap the kettle in a couple old blankets or a sleeping bag and forget it for 60-90 minutes. if you insist on using a cooler, convert it to a mash tun and do a traditional mash.
if you have a large enough kettle, I would suggest skipping the cooler. just wrap the kettle in a couple old blankets or a sleeping bag and forget it for 60-90 minutes. if you insist on using a cooler, convert it to a mash tun and do a traditional mash.