Temperature drops in mash tun?

Last night I brewed for the second time, an all-grain American Wheat beer. Everything thing went really smoothly and I hit my OG number okay.

But there's something about the mashing I didn't quite understand. I was tracking the mash temp with a probed thermometer : http://www.amazon.com/Taylor-1470-Digital-Cooking-Thermometer/dp/B00004XSC5/ref=sr_1_1?ie=UTF8&qid=1330111438&sr=8-1 (which I thoroughly recommend to anyone who is still using the floaty style thermos!!). To my delight, the first 20-30 min. of the mash, I stayed at 151 F, 1 degree below my target 152 F. Around 35 to 40 minutes in, it dropped to 150 F so I boiled a quart of water and dumped it in and stirred it around. To my surprised, the temperature dropped to 149 after a few minutes and as I boiled another quart, it dropped to 148.

Was the probe just in a warm spot? Or did me opening the cooler affect it that dramatically? I also noticed my mash paddle was sitting on the sink, so maybe it was cool, too. Is a 3-4 F drop in temp so bad this late in the mash?

I'm sure my brew will turn out, but I just got to thinking about this stuff and would like your thoughts.

are you using a cooler? stirring is the best way to cool something down.

Are you using a drink cooler? I use a 5 gallon drink cooler for mashing and see a couple degrees difference from the bottom to the top. Best thing I found was to preheat the cooler then aim a bit high on the temp then stir till it comes down to temp.

Did you have some kind of blanket on the lid of your tun? I would say that you did lose heat when your tun was opened and the mash was stirred. You may have lost heat through the lid of your tun as well.

IMO you are worrying too much about a temp drop of the mash. Most of my beers mash at 152 and drop to between 146 and 148 over the course of an hour. I've done an iodine test for conversion and it comes up negative at 20 minutes.

Bottom line is a drop of a few degrees over an hour is acceptable in my mind. I don't think I'd even start worrying until I lost 10 degrees with the first 20 minutes.

I find im my 10 gallon drink cooler I can move my temperature prob around in the grain bed and find a temperature change of 4 to 5 degrees. I just try to hit the temp as close as I can have a brew!

Opening the lid immediately loses heat. Just leave it closed next time.

Oh okay. Like I said, I wasn't too worried about 4 deg after 50 min. With stirring and opening. But yeah, I might just leave it closed next time unless I'm going to add 2 quarts of boiling water or something.

I'm having trouble cooling the wort in my fermenter now. I'm adding ice bags, but it's at 85/86 F degrees now and hasn't started bubbling through the blow-off hose. Will it at this temeperature? I'm trying to get it to 72...