Mash tun heat loss

[jcw203]

I have a 10 gallon Rubbermaid cooler that I am using as a mash tun I keep having about 4-5 degrees of heat loss during a 60 minute mash. Does anyone else have this much of a problem with heat loss and what did you do about it. Also I was starting my mash all stirred took temp right before I put my lid on at 154 it was 75 degrees outside and I have a push on lid not a screw top but it doesn't leak either.

 

[Gartywood]

How long does it take for the temp drop to show up? I lose 1-2 degrees max in an hour mash. I can think of two possible issues. The first is that it can take 5-10 minutes for the temp to stabilize so if you stir for a couple of minutes take a temp and close it you might not actually have a stable accurate reading. The second is fill level of the tun. If you're doing a 3 gallon strike volume in the 10 gallon tun all of that headspace can allow for a lot of heat loss