Mash tun heat loss

I am getting started with all grain and I built a mash tun out if a 48 qt igloo ice cube cooler. I noticed the lid was not insulated so I drilled some holes in it and put spray foam in there. Did a few different tests to see how it holds heat with 3 gallons of water at 160 degrees and also pre heated the tun. Im losing about 8-10 degrees over an hour. that seems like alot, from what ive read most people only lose a couple degrees over an hour. My question is does the temperature stay more stable with all the grain mixed in or should i get a better cooler.

I suspect you didn’t preheat the cooler before your test. Also, you should realize that water will loose heat faster than an actual mash. I have the same cooler and this is my procedure - I heat my strike water about 8-10 degrees over my desired mash temp and wait for it to drop to where I want. Over the course of 60 minutes the temp usually drops 3-4 degrees depending the size of the mash, though after about 15-20 minutes it is pretty stable. Oh, and I never filled the lid with foam. I’ve been meaning to, but after 7 or 8 years I guess it isn’t going to get done.

The preheating advice above is spot on. A container filled to 25% capacity with water is not going to be as stable as a higher volume which also includes grain.

How are you measuring temp?

i did pre heat kind of. i started with 3 gallons of 174 degree water and dumped it in the cooler. let it sit for 10 min, took temp again which was 164, then started 1 hour timer. i have an expensive fluke meter with a temperature probe for measuring temp. im guessing that its pretty accurate.

I don’t know why I didn’t think of this earlier, but my brewing software has a procedure to calibrate the heat capacity of your vessels. So I looked at the data from my last calibration. The ambient temp was 72ºF and I used five gallons of water at 160. After five minutes the temp had dropped to 158. After 65 minutes the temp was 152. So that’s a six degree drop in an hour. Taking into account that I used more water than you did I’d say your results of an 8-10 degree drop are comparable,so I think you’re fine.

thanks for the input. i think i will try a few batches and see how it goes. i know alot of people use this type of cooler so it can’t be that bad