Difference in Dome vs Digital Thermometer

[TitanMan]

I have been smoking for a while and have several grills, but I'm fairly new to Kamado Joe.  I am including some photos of the difference in temperature between my dome thermometer and the Thermapro that I am using to monitor the grill.   Is this difference normal?  Which one is more likely to be correct?  This is not the largest difference I've seen and it makes a big difference on how the meat will cook depending on which one is correct.  The Thermapro probe is attached to the grill just in front of the meat.

[St1brew]

First of all, welcome aboard! I think it is normal for some deviation in temps from grate to dome. I would trust the grate probe as far as a more accurate temp goes. However, in my experience the difference isn't going to change much in the end. You are still cooking the meat to some internal temp/probe tender. You simply adjust your vents to allow less air into the coals and wait a bit. This may also be a cause of opening the dome. I'm sure there is a temp calibration video around here as well. That may help. Some people use an temp controller. Good luck and enjoy the new grill!

[TitanMan]

I don't think it will make a big difference on high temp cooks, but I do a lot of low and slow and the difference 339 and 275 is quite a bit there.  One of the reasons I asked is because when I  tried my first brisket on the Joe last week, it had a good flavor but I definitely felt like it was overdone.  The internal temp was on target, but I felt like it cooked too fast.  I really bought this grill for higher temp cooks, but I'm just trying to figure out how it does on the low and slow.

[moloch16]

Them mechanical thermometer is probably a cheaper version and will be less accurate.  There are better mechanical models available you could swap in, but may not be worth the money and effort when you already have a digital thermometer.  Also, where the probe is placed will have a lot to do with the reading.  I recommend keeping a probe at the grate and go by that reading.  I'm still mastering briskets, mine have turned out dry and overdone.  The brisket flat has very little fat to keep it moist.  My next attempt I plan to smoke it for 4-5 hours and then the remainder of the cook will be wrapped to allow it to bask it the juices to keep it moist.

[TitanMan]

56 minutes ago, moloch16 said:

Them mechanical thermometer is probably a cheaper version and will be less accurate.  There are better mechanical models available you could swap in, but may not be worth the money and effort when you already have a digital thermometer.  Also, where the probe is placed will have a lot to do with the reading.  I recommend keeping a probe at the grate and go by that reading.  I'm still mastering briskets, mine have turned out dry and overdone.  The brisket flat has very little fat to keep it moist.  My next attempt I plan to smoke it for 4-5 hours and then the remainder of the cook will be wrapped to allow it to bask it the juices to keep it moist.

I have had very good luck with briskets using the methods I learned from Malcom Reed at How to BBQ Right. He does wrap in the middle of the cook.  I think the one I tried on the Big Joe was overdone because I was going by the dome thermometer and so I wound up cooking it way to fast.  I appreciate the advice and I'll have to try again using the probe temp at the grate.

[St1brew]

I was suggesting using the grate probe as well, just shut the vents a bit until you settle at your desired temp. Keep in mind this may take awhile as the ceramics hold in heat like a champ.

Edited March 23, 2019 by St1brew
grammar

[BobE]

Welcome to the Guru TitanMan. 

The Therm Pro uses a K type thermocouple (TC) in the probe and some electronics in the base unit to provide the temperature.  I use TC's all the time and would advise that you trust the Therm Pro for an accurate reading.  Dial type thermometers use a coiled up bi-metal strip to measure temperature.  Over a limited range they are okay, but they aren't linear over a range of several hundred degrees 

 

I've tested my KJ dial thermometer and Therm Pro probes against a certified Fisher Scientific mercury bulb thermometer over a range of 150 to 215F and found that the Therm Pro probes are accurate to abour 1 deg F.  The KJ dial thermometer is was off at the low range but very close at the top of the range I tested. 

 

If you want to calibrate the dial over an extended temperature range here are the steps I'd use:

 

Remove the dial thermometer from your grill using a 1/2" wrench on the nut inside the dome.  Gently tighten it when you reinstall so you don't risk cracking the ceramic. 

1. Heat a small pot of peanut oil up to 200F using the ThermPro to measure the temperature (I don't recommend getting the wires wet).  You will need enough oil in the pot to completely submerge the dial's probe up to the threads.   
2. Put the dial probe, up to the threads, in the oil for a few minutes and record what it reads. 
3. Heat heat the oil up to 300F, again using the TermPro probe to monitor the temperature
4. Repeat step 2
5. Raise the oil to 400F *. 
6. Repeat step 4

Now you have a 3 point calibration.  You can adjust the Dial thermometer by tweaking the screw in the back of the dial so that it is accurate at one temperature.  I adjusted mine to be spot on at 250F because that's close to what I'm looking for most of the time.  

 

*The smoke point for refined peanut oil is around 440-450F.  Don't go that high unless you like the sound of smoke detectors.  There are other oils that have a higher smoke point.

https://en.wikipedia.org/wiki/Template:Smoke_point_of_cooking_oils

 

Best of luck and if you do this, be careful with hot oil, let it cool down to room temperature before you remove it from the pot.

[TitanMan]

5 minutes ago, BobE said:

Welcome to the Guru TitanMan. 

The Therm Pro uses a K type thermocouple (TC) in the probe and some electronics in the base unit to provide the temperature.  I use TC's all the time and would advise that you trust the Therm Pro for an accurate reading.  Dial type thermometers use a coiled up bi-metal strip to measure temperature.  Over a limited range they are okay, but they aren't linear over a range of several hundred degrees 

 

I've tested my KJ dial thermometer and Therm Pro probes against a certified Fisher Scientific mercury bulb thermometer over a range of 150 to 215F and found that the Therm Pro probes are accurate to abour 1 deg F.  The KJ dial thermometer is was off at the low range but very close at the top of the range I tested. 

 

If you want to calibrate the dial over an extended temperature range here are the steps I'd use:

 

Remove the dial thermometer from your grill using a 1/2" wrench on the nut inside the dome.  Gently tighten it when you reinstall so you don't risk cracking the ceramic. 

1. Heat a small pot of peanut oil up to 200F using the ThermPro to measure the temperature (I don't recommend getting the wires wet).  You will need enough oil in the pot to completely submerge the dial's probe up to the threads.   
2. Put the dial probe, up to the threads, in the oil for a few minutes and record what it reads. 
3. Heat heat the oil up to 300F, again using the TermPro probe to monitor the temperature
4. Repeat step 2
5. Raise the oil to 400F *. 
6. Repeat step 4

Now you have a 3 point calibration.  You can adjust the Dial thermometer by tweaking the screw in the back of the dial so that it is accurate at one temperature.  I adjusted mine to be spot on at 250F because that's close to what I'm looking for most of the time.  

 

*The smoke point for refined peanut oil is around 440-450F.  Don't go that high unless you like the sound of smoke detectors.  There are other oils that have a higher smoke point.

https://en.wikipedia.org/wiki/Template:Smoke_point_of_cooking_oils

 

Best of luck and if you do this, be careful with hot oil, let it cool down to room temperature before you remove it from the pot.

Great info!  Thank a lot!

[John Setzler]

Go by the dome thermometer.

[TitanMan]

11 minutes ago, John Setzler said:

Go by the dome thermometer.

Okay...now I'm really confused.  By the way, love your videos. I've already made some great pizza after watching you do it. 

[John Setzler]

12 minutes ago, TitanMan said:

Okay...now I'm really confused.  By the way, love your videos. I've already made some great pizza after watching you do it. 

 

I always cook by dome temperture and I have never had any problems.  You will always have variations on grate level probes based on where you put them.  If you can put a grate level probe in the CENTER of the grill at least 2" above the meat, then you should get a relatively reliable reading from it.

[landscaper]

Now I'm hungry for a donut!

[Chasdev]

I've found that temps at cook grate level and up in the dome change from exactly the same to wildly different at different times during a cook.

I've got a high dollar analog gauge twinned with an accurate digital probe and they always read exactly the same, but they rarely agree with the digital probe/s I place at and just under the cook grate.

Not to mention that after preheating, even if all the readings match up perfectly, once you place a 8 or 12lb slab of room temp (or colder) meat on the cook grate, all readings quickly agree to disagree.

 

 

[SeaBrisket]

I only use my probes for overnight cooking on my KJ Classic, basically to have an alarm in case the temp goes way off target. I find that the dome thermometer is initially way off at the start of the cook but that the two thermometers get closer to each other as the heat sinks into the ceramic.

 

Additionally, I find that in the middle of the cook, the grill level thermometer will tend to swing wildly in comparison to the dome thermometer, which stays relatively constant. For this reason, I tend to trust my dome thermometer more. When I cook during the day and can closely monitor the grill, I usually just skip the grill level thermometer and trust the dome. Other brands' dial thermometers might not be as good, but I trust the KJ.

[dman]

Like John says, just go by the dome temp. On my Big Joe my dome temp is 40-50 degrees lower than the grate temp. The meat is usually done when it probes tender, not at any particular target temp. I’ve had buttstender at 200 and 220. All done at 275-295 dome temp in 4-5 hours. Just experiment until you get used to it and have fun.