Trying to understand varying EHERMS mash temps

[BrewMehr]

I'm on my 3rd brew since installing a thermocouple on the outlet of my mash tun. Picture below

The thermocouple is actually only 0.50" deep and I made my own thermowell by running an end mill 0.50 into a 1/2" NPT plug. The plug is 1.27 deep so the thermocouple is not actually in the fluid flow.

The problem I am seeing is that readings from this thermocouple are about 10* below what I would expect. The brew I have going right now mashed in at 153* as confirmed by placing a contact thermometer in the center of the mash. Yet the moment I begin recirc, the outlet thermocouple reads 143*.

Is it possible that the bottom of my mash is indeed 10* cooler than the top? Or is it more likely that my thermowell setup is giving me an off reading? When I installed the thermocouple I made sure it made contact with the bottom of the thermowell. I can't imagine how there could be a 10* temp difference from the center of outlet flow vs the edge where the thermowell is.

If I take a temp reading of the hoses on the outlet with an IR temp gun, I get numbers that are just below the thermocouple readings. This makes me think the thermocouple could be accurate. But that would mean the bottom of my mash is 10* cooler than the center only 20 minutes after mash in.

Has anyone else experienced this?

TIA

 

[acidrain]

Yes, temperatures vary wildly from area-to-area.. especially at extremities like bungs/output ports.
It's extremely hard to maintain a uniform temperature without extensive insulation.
I have this same issue even though my SS MT is insulated. A Rubbermaid cooler actually works better for this, but I hate plastic.

 

[Ozarks Mountain Brewery]

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