DIY Mashtun Thermowell - easy and cheap

**Walker** · 01-13-2010, 04:26 AM

I wanted to put a thermowell on my mashtun so that I could check the temp without having to keep opening the lid and losing heat. The thermowells I found online were more expensive than I wanted to pay, so......

Here's what I used:
(1) 1/4" OD copper tubing (about 8 inches of it) - $1.25
(2) 1/4" FIP x 1/8" brass compression coupling - $1.75
(3) 2" long 1/8" MIP brass pipe nipple (shank) - $2.00
(4) 1/8" FIP brass coupling - $2.25 (*see below)
(5) two 3/8" stainless steel washers - $0.75
(6) o-ring - $0.25

Total cost = $8.25

(7) are my probe thermometers - I already had these, so not counting their cost.

* = I really didn't want that freaking coupling. All I wanted was a threaded 1/8" brass pipe cap or a simple nut that would thread onto the shank from the outside, but they didn't have either of those things at Lowe's. I bought the coupling just to get the hell out of the store.

I took a lot of pictures as I did this and am about to post them, so here goes....

**Walker** · 01-13-2010, 04:28 AM

I started by drilling a 3/8" hole through the wall of my mashtun.

Then I shoved the shank through the hole (it was a TIGHT fit and I almost had to hammer it through). The shank was just barely long enough to fit through the wall of the cooler, and I left a little more threading exposed on the inside compared to the outside.

To seal everything on the inside, I wrapped the threads with teflon tape and pushed an o-ring onto it as far as I could.

On the ouside, I just needed a nut and washer here so that I could get the opposing force necessary to mash my seal on the inside later. A simple nut or a 1/8" pipe cap with a hole drilled in it for the probe would have been great, but I was stuck with a coupling. I put it on just hand-tight at this point.

Addng this port through the tun wall was the hard part.

**Walker** · 01-13-2010, 04:30 AM

To make the rest of the well, I cranked the compression fitting onto one end of the copper tube until it squealed like a piggy and made a solid connection to the tube.

I measured how far my small digital thermometer probe would stick through the shank and cut the copper tube a couple inches longer than that, just to give myself some room to play with incase my next probe thermometer was longer. I had considered just making it long enough for that really long probe thermometer from the first picture, but that would have needed a well that extended all the way across the diameter of the tun (which would have made getting my false bottom in and out a challenge).

This tubing is soft, so I just crimped the end of it closed with my vice.

**Walker** · 01-13-2010, 04:34 AM

Now it was time to tighten everything for my seal. I took the compression fitting back apart and threaded the FIP part onto the shank inside the tun, using a stainless steel washer between the connector and the o-ring. The I turned both the coupling on the outside and the fitting on the inside with wrenches to compress everything together and mashed the o-ring.

A little more teflon tape on the male part of the compression coupling, and we're good to go.

And then I threaded on the crimped copper tube to complete the inside work.

The shank had an ID the same size as the OD of my copper tube, so I cut another small piece off and hammered it through the shank/coupling from the outside to make a tighter input port for the probe.

**Walker** · 01-13-2010, 04:34 AM

And that's it.

I tested it all out with hot water, and there are no leaks anywhere that I can see. The probe in the well reads +/- 0.1*F compared to the same probe placed directly into the water. I can live with +/- 0.1*F.

**arturo7** · 01-13-2010, 04:38 AM

Nice work, mom!

**Walker** · 01-13-2010, 04:44 AM

Thanks, sonny.

It only took about an hour total for this (about the same amount of time it took to re-size the images and do the write-up).

I'm adding one to my keggle tomorrow night.

**Walker** · 01-13-2010, 05:11 AM

Quote:

Originally Posted by Walker

I tested it all out with hot water, and there are no leaks anywhere that I can see.

Curses! There is a leak. A very very very slow one. Water is getting into the well. I need to disassemble and figure out if it's getting into the foam of the cooler.

Poop!

**Walker** · 01-13-2010, 05:55 AM

I didn't have the compression screwed onto the shanl tight enough.
Water was able to get into the well, but no water was leaking past the o-ring into the insulation inthe cooler's wall.

Seems solid now!

Hermit · 01-13-2010, 06:27 AM

You might consider soldering the end closed just to be safe.

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