Mounting a thermometer is one of the most common modifications
made by Weber Smokey Mountain Cooker owners. This topic provides the detailed instructions you need
for a professional installation.
always...click on any of the pictures to
view a larger image.
Do I Want To Drill A
Hole In My Beloved WSM?
This is the first
question you should ask yourself. Measuring
Temperature In The WSM provides a thorough discussion of all
the options you have for measuring temperature in your cooker, including
approaches that don't require you to drill holes. For example, you can
insert a thermometer through the
lid vent (Picture 1) or use a
probe thermometer to measure temperature at the cooking surface (Picture
should not undertake this modification unless you're comfortable working with power tools and you're
willing to accept the risk that you might screw things up. Also, mounting
a thermometer may void the warranty on your WSM, so take this into
consideration before proceeding.
Finally, when drilling a hole in
your WSM, make sure to wear eye protection since bits of porcelain
enamel and steel will fly in all directions.
Where Should I Mount A
You can mount a
thermometer in the lid or in the middle cooking section. Some people mount
them in both locations. In my opinion, the lid is the best place for
The most common lid location
is on the
other side of the handle opposite the vent. This is where I chose to mount
my thermometer. Other popular locations are halfway between the handle and the edge of the lid, or
very close to the edge of the lid, to get a reading just above the top cooking grate.
When mounting at the edge
of the lid, make sure to install the thermometer far enough above the edge
so the dial won't hit the ground when you set down the lid.
For the middle cooking
section, the most common approach is to mount a thermometer just above the
lower grate. This is done by drilling a hole in the body of the middle cooking section
itself, and less frequently by drilling through the access door.
One creative approach
that does not require drilling is to remove the top nut and
bolt from one of the grate brackets and inserting a thermometer through the
resulting hole. This allows you to measure the temperature just below the
top cooking grate.
The two most common types
of thermometers to mount in the WSM are candy thermometers and
industrial-grade thermometers. Installation of each type is described
Mounting A Candy
To mount a candy
thermometer, drill a hole just large enough to accommodate the
diameter of the stem. If you make the hole the right size, you will
have a good fit and little smoke leakage.
matter whether you drill from the outside or inside surface. If you're
careful and use a sharp bit, you'll end up with a clean hole and very little chip-out of the finish around the hole.
You can put several
layers of masking tape over the spot you want to drill, which will keep
the drill bit from wandering. Some people feel this also minimizes
chip-out during drilling, but I've not noticed any difference with or
The stem of a candy
thermometer is not threaded and will not screw into the hole. To prevent it from falling out accidentally,
hold it in place with
an alligator clip (Picture 2), an "e" clip (Picture 3), or a set
The Weber #9815 Replacement Thermometer used in Weber gas grills can also be mounted using
this method and can be purchased at most stores selling Weber grills.
thermometers have a male 1/2" NPT (National Pipe Thread) mounting base
on the backside of the dial, as shown in Picture 1. There are two ways to mount this
type of thermometer in the WSM.
The first approach is to
make a hole just big enough so you can screw the thermometer into the
cooker—let's call this the "screw-in" approach. The second
approach is to make a hole slightly larger than the thermometer's threaded
base and fasten the thermometer to the cooker using a lock nut—let's call
this the "lock nut" approach.
I prefer the lock nut
approach because it results
in a professional looking installation and I can easily remove the
thermometer for testing, recalibration, or replacement without
damaging the cooker. With the screw-in approach, I'm afraid that I'll chew
up the hole after screwing the thermometer in and out a few times.
Below are the
detailed steps to implement the lock nut approach. At the end of
this page I'll explain how to do the screw-in approach.
Regardless of the
approach you choose, you'll need to make a big, perfectly round hole in
your cooker. I've learned about two different tools that make
the job easy—the step drill bit and the knockout punch. Either tool will
do a good job for you.
Unibit #4 Step Drill Bit has a series of 1/16" graduated steps to drill holes ranging from
3/16" to 7/8". Its standard 3/8" shank fits most electric
Unibit makes a very clean hole with little or no chip-out of the finish, especially in the lid where the surface is curved
both horizontally and vertically. It also makes the hole in a single shot,
whereas the knockout punch requires a two-step process. The Unibit is
readily available at better hardware stores.
The disadvantage of the
Unibit is that it's pricey—about $40. However, it's a tool that
you'll probably find other uses for on future projects.
Electricians use a
knockout punch to cut holes in electrical boxes in order to
connect conduit. It consists of a
cup-shaped die and a cutting head (the punch) that run along a threaded shaft.
The punch is removed from the shaft and the shaft is inserted through a
pilot hole drilled in the metal surface. The punch is screwed back onto
the shaft and when the shaft is tightened, the die and punch
are pressed together through the metal, creating a perfect 7/8"
makes a 7/8" knockout punch for 1/2" piping that is sold through industrial product suppliers such as
The advantages of the
knockout punch are that it's a less expensive tool—about $25—and it is
easier to use for the washer-enlarging process that's discussed further
down this page.
The disadvantages are
that it can be a difficult tool to find and it can only be used for one
thing—making 7/8" holes. It makes a clean hole, but not as
clean as the Unibit. It will produce a small amount of chip-out of the
porcelain finish around the hole.
The knockout punch also
requires a two-step process—you must drill a 3/8" pilot hole using a
regular metal drill bit, then install the punch and proceed to cut the
Unibits and knockout
punches are commonly used by electricians, so if you're lucky enough
to know an electrician you might be able to borrow these tools or
have them punch the hole for you.
Parts & Tools List
For The Lock Nut Approach
Here's what you'll need
to accomplish a thermometer installation using the lock nut approach:
thermometer with male 1/2" NPT threaded mounting base;
operating range 50-550°; stem between 2-1/2" and 6"
- 1/2" or
3/4" steel washer, about 1-3/8" in diameter
- 1/2" lock nut
- Flat black
high-temp barbecue spray paint (optional)
- Masking tape (optional)
- Unibit #4 step
- 1/2" NPT conduit knockout
metal drill bit
- Bench vise or
- Electric drill
- Eye protection
industrial-grade thermometers in a variety of stem lengths, dial sizes,
and temperature ranges. They cost $30-40 and can be purchased from
You can buy the washer, lock nut,
spray paint, and masking tape at a hardware store. If you'll be using
the Unibit, buy a washer with a 3/4" hole in it; if using the
knockout punch, buy a washer with a 1/2" hole in it. You'll find
steel lock nuts in the electrical department and brass versions at
specialty fastener suppliers.
Enlarging The Hole
In The Washer
The washer serves
as a backing plate to help stand the thermometer off the
surface of the cooker. The 1-3/8" diameter ensures that any
chip-out of the porcelain finish will be covered.
If you're using the
Unibit, clamp the washer to a piece of scrap wood and enlarge the
hole to 13/16", then ream the hole a little so the washer slides
over the threads on the thermometer mounting base. The result is shown
in Picture 1
If you're using the
center the punch on the 1/2" washer and hold the punch firmly with plumbing
pliers or in a bench vise while you tighten it. The result is shown in
Picture 2—the distorted piece on the
right is the bit removed by the punch.
The washer shown in
Picture 2 is 3/32" thick and was
pretty hard to punch. You could use a thinner washer or several thinner
together, just make sure they're about 1-3/8" in diameter.
Making The Hole In The Cooker
Now's the time to
finalize your decision on where to mount the thermometer in your cooker.
I chose a spot on the
lid opposite the vent.
The process described below is the same regardless of the location you
If you're using the
Unibit, just drill the hole to 7/8". Put several layers of masking tape
over the spot you intend to drill to keep the bit from wandering, then
start drilling carefully. If you prefer, drill a pilot hole first with
another drill bit before making the final hole with the Unibit.
If you're using the
knockout punch, drill a 3/8" pilot hole as shown in Picture 1. As
with the Unibit, place several layers of masking tape over the spot
you'll be drilling to keep the bit from wandering.
Next, install the knockout punch through the pilot hole. It doesn't
matter whether you put the cutter on the inside or outside surface of
the cooker—I've done it both ways and gotten the same result.
Picture 2 shows the
punch cutter installed on the outside of the cooker (the work bench is at
the bottom of the photo and the cooker lid is at
the top, resting upside down on the work bench). Picture 3 shows the
view inside the lid. Cutting the hole is as simple as tightening the
punch slowly with the wrench.
Picture 4 shows the
resulting hole viewed from the outside of the lid. You'll notice there's
some chip-out of the finish all around the hole.
Picture 5 shows two
test holes I made in a damaged charcoal bowl that I keep around for just
this purpose. The punched hole is on the left and the Unibit hole is on
the right. If you click the picture to enlarge the view, you'll notice
that the Unibit hole is much cleaner. Please note that the lighting in
this picture makes the punched hole look worse than it is in reality.
Touching Up The
As an optional step,
you can mask the area
around any chip-out and spray on a few light coats of high-temp barbecue paint.
This will protect any bare metal from potential rust. The paint won't be
visible afterward because it will
be completely covered by the washer.
Picture 1 shows how
the washer slides fits over the threads on the thermometer mounting
base. I put the lock nut on part way to illustrate how the pieces fit
together. The lid will be between the washer and the lock nut.
To install the
thermometer, slide the washer over the threads and insert the
thermometer through the hole in the cooker, fastening securely with the
lock nut. Do not over tighten the lock nut.
To remove the
thermometer for testing, calibration, or replacement, simply remove the lock nut. If you decide to remove the thermometer
permanently, you can plug the hole using a stainless steel knockout plug
found at hardware stores.
Picture 3 shows how the
thermometer looks on my WSM. Picture 4 shows the washer between the thermometer and the lid.
Picture 5 shows the inside of the lid with the thermometer stem and lock
About The Screw-In
To screw an
industrial-grade thermometer directly into your cooker, start by
drilling a 3/4" hole using the Unibit described above. With the
hole drilled, try screwing in the thermometer. Since the hole in the
cooker is not threaded, it will be a very tight fit. If the hole is
too small, enlarge the hole ever so slightly. This
takes a gentle touch—you've only got one chance to make this hole just
the right size.
If you end up making
the hole too big and the thermometer threads slide right through the
hole, you can revert to the lock nut approach described above.
More Installation Ideas
To see examples of
thermometer installations sent in by TVWB readers, visit
More Thermometer Installations.
This is a great looking
modification if you have the courage to poke a hole in your cooker!
Take things slowly and use your common sense. But remember, you can get
equally good results by sticking a thermometer through the lid vent or
placing a Polder probe on the cooking surface. What's important is that
you measure the temperature of your cooker in some fashion.
Good luck and have fun!
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