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Back in the dark ages...before 2009...if you owned a Weber Smokey Mountain Cooker and wanted a thermometer, you had to add install yourself. You could stick one through the lid vent, you could drill a hole and mount one in the lid, or you could run a probe thermometer under the edge of the lid or through a grommet in the side of the cooker.
But Weber was paying attention to what customers were doing, and starting with the 2009 model year, they added a 2.25" thermometer with a 1.5" stem to the lid of the Weber Bullet.
When I first published this article in 2001, installing a thermometer in the lid was one of the most common modifications made by Weber Smokey Mountain Cooker owners. That's not the case today, but if you acquire a pre-2009 WSM and want to add a thermometer, or you have a newer model and want to replace the stock thermometer with a larger industrial-grade unit, then this topic provides the detailed instructions you need for a professional installation.
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 or slip a probe thermometer under the lid or through a grommet to measure temperature at the cooking grate.
You 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. Drilling holes in your WSM may void the manufacturer's warranty, so take this into consideration before proceeding. Also, when drilling a hole in your cooker, make sure to wear eye protection since bits of porcelain enamel and steel may fly in all directions.
You can install a thermometer in the lid or in the middle cooking section. A few people mount them in both locations. In my opinion, the lid is the best spot to get an overall temperature reading of your cooker.
The most common lid location is on the other side of the handle opposite the vent. This is where Weber mounts the stock thermometer and it's where I always mount thermometers on older WSMs.
For the middle cooking section, the most common approach is to install a thermometer just above the lower cooking 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.
Since lid installation is most popular, that's what we'll focus on in this article, but the process for installing in the middle cooking section is basically the same as for the lid.
To install an industrial-grade thermometer, you'll need the following:
The thermometer shown here is the Tel-Tru BQ300 with a 100-500°F operating range, 3" dial and 4" stem. It sells for about $45 plus shipping. The shorter 2.5" stem is preferred, but I've used a 4" stem for many years and never had a problem with clearance between stem and meat.
Industrial-grade thermometers have a male 1/2" NPT (National Pipe Thread) mounting base on the backside of the dial. To fasten it to the lid, you'll need a 1/2" steel lock nut. These lock nuts are used to connect rigid metal conduit to electrical enclosures and boxes and you'll find them at the hardware store in the electrical department for just a few cents. Brass versions are available at specialty fastener suppliers. For an online option, Amazon sells a Tel-Tru Thermometer Installation Kit that includes both the washer and lock nut.
To determine the spot to drill, apply some painter's tape over the approximate area where you will mount the thermometer (Photo 2). Measure 5" down from each side of the metal lid handle to a point where both measurements cross (see an example in Photo 16 below). Mark the spot with an "X" (Photo 3).
To drill the hole, use a center punch at the "X" to create a spot for the drill bit to grab (Photo 4). Use a 3/4" metal hole saw to make the hole (Photos 5-6). Remove the painter's tape.
As an optional step to prevent rust, use painter's tape and newspaper to mask just outside the hole and apply two coats of high-temp barbecue paint (Photo 7). Let paint dry.
To fasten the thermometer, slip the washer over the thermometer stem (Photo 8) and insert the stem into the hole. Thread the lock nut onto the thermometer's threaded base and tighten until finger tight (Photo 9). Rotate the dial face so it's properly positioned (Photo 10) and tighten the lock nut using pliers. Do not overtighten.
To install a stock thermometer, you'll need the following:
Start by breaking off the bezel tab. On a new WSM, this tab fits into a slot in the lid that locks the bezel in place, and the tab hole accepts a tab on the back of the thermometer that aligns the dial face and keeps it from spinning around. Use pliers to snap it off (Photos 13-14).
To determine the spot to drill, apply some painter's tape over the approximate area where you will mount the thermometer. Measure 5" down from each side of the metal lid handle to a point where both measurements cross. Mark the spot with an "X" (Photo 16).
The thermometer's threaded mounting base measures 0.369" (Photo 17), so you'll want to drill a 3/8" hole.
Use a sharp 1/8" metal drill bit to make an initial hole. Switch to a Unibit #4 step drill bit (Photo 18) and finish the hole (Photo 19). Using the 1/8" drill bit first eliminates the need to use a center punch. Remove the painter's tape.
Insert the thermometer into the bezel and insert the stem into the hole. Hold in place by hand or with tape (Photo 20) and thread the wing nut onto the thermometer's threaded base and tighten until finger tight. Do not overtighten. Rotate the dial face so it's properly positioned (Photo 21).
Special thanks to TVWBB member Joe F for providing these steps and photos for mounting a stock thermometer.
To install a candy thermometer, locate the spot for drilling as shown in either of the methods described above. Use a sharp metal drill bit to make a hole the same size or just slightly larger than the diameter of the thermometer stem.
The stem of a candy thermometer is not threaded and will not accept a lock nut or wing nut. To hold it in place, fasten with a piece of cork (Photo 25) or an "e" clip from the hardware store (Photos 26-28).
Some people like the greater accuracy or the larger, easier-to-read dial of an industrial-grade thermometer. If you own a newer WSM with a stock thermometer and want to upgrade to an industrial one, it's simply a matter of enlarging the stock hole to 3/4" using a 3/4" metal hole saw or Unibit #4 step drill bit and installing the thermometer, washer, and steel lock nut as described earlier in this article.
If you decide to remove a thermometer permanently, you may be able to plug the hole using a steel knockout plug found at the hardware store (Photo 29).
These are all good 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 probe thermometer on the cooking grate. What's important is that you measure the temperature of your cooker in some fashion and do it consistently, so you have a sense how your WSM operates. Good luck and have fun!
Stock thermometer install photos: 2014 by Joe F