Jade_The_Raw

Recipes 

How would I go about doing this?

day_trippr

Recipes 

Leaving aside the actual utility of a fixed thermometer in a mash tun...I would start with a simple bulkhead like this one from BrewHardware.com.


As there's no loss in trying, I'd see if it held a seal through both inner and outer cooler walls - ie: the outer washer and nut on the outside of the outer wall. But at the first sign of trouble caused by squishing the walls together, I would cut a larger hole in the outer wall to clear the washer, and run the outer nut and washer snug against the inner wall. That would totally remove the whole Squish Factor from the leakage equation...

Cheers!

FuzzeWuzze

Recipes 

Acquire digital thermometer with a long wire lead for $20 at Walmart/Target/etc

Shrink heatwrap onto the end or some other method of waterproofing the tip where the wire joins.

Stick in mash tun, screw on lid.

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Arduino Real Time Fermentation Monitor

Fuzze Logic Brewing - Current Fermentation Temperatures

amandabab

Recipes 

use a bargainfitting weldless kettle bulkhead (the close nipple kit)

drill a 1-1/2" (for working room)hole through the OUTER plastic and insulation only
drill a 13/16" hole through the inner wall

with the inner wall of the cooler exposed install the kettle bulkhead with the o-ring and locknut on the inside and the female coupling on the outside.

screw a 4" bargainfittings thermowell into the female coupling

fill the area with expanding foam

add the thermometer and it will be almost flush with the outer wall.
its mashpaddle proof and doesn't rely on compressing the insulation to seal

Dougie63

Recipes 

williams brewing.com sells a thermometer that is made for a cooler for like 14.99

Brewskii

Recipes 

...But it gets bad reviews for leaking.

I started a thread on this long ago and I decided hanging my kitchen aid remote just into the mash and holding it there by trapping the wire in the lid vent lines was good enough for me(if you submerge just the metal on the probe it works just fine even though it's not waterproof). That and enough measurements gave me some faith in the beersmith thermal calculations so I'm more apt to look at the temp and accept that what it is is what it is.
Not the best for repeat ability but, less stressful.
That being said, amandabab's solution is genius for that type of set-up. If your doing infusions in your cooler it's pointless to try to make temperature corrections. You'll do more bad than good. But it is important to know what your mash temps are. I just thought the negatives of breaching the cooler side wall out weighed the positives for having a dedicated thermometer in it.