Was doing a 10 gallon batch Saison this weekend. Target mash temp was 147. Preheated 48 qt cooler mashtun with 200 degree water. Drained, put in 25 lbs grains. Added 162 degree water to achieve target temp. After stirring to make sure there was no dried grain, took temp and got 142. Let it sit for 10 minutes and it was still 142. Added 3 qts of 190 water and got temp up to 145. Waited another 30 minutes and was only at 145. This is where I got "creative". I was essentially out of room for more water in the mashtun, so I drained off about 2 gallons of wort and brought it up to 200 degrees and added back to the mashtun. Hit 149-150 after stirring. Let it sit for a total rest of 85 minutes. Seemed to have worked in that I hit an OG of 1.075 after a 90 minute boil (aiming for 1.065).
Has anyone else ever had to do this? Just curious, since I have never read about drawing water out of the mashtun, without the grains as well, in order to raise the temp in the mashtun. (I know decoction mashing entails taking grain and water out of the mashtun.)