Weird Temp Readings...


 
D

D Arita

TVWBB Fan
I'm doing a butt cook and decided to put my ET732 probe in the top vent to get more accurate readings. For the first few hours, the 732 was reading a consistent 10 degrees higher than the lid thermometer. About 6 hours into the cook, the 732 suddenly started going up, up, up and is now reading about 30+ degrees higher than the lid therm. What's up with that?
I did a vent adjustment and the lid therm went down about 10 degrees...at the same time, the 732 temp crept up a couple of degrees. What's going on?
 
Personally I always do my temps @ top vent.
Starting to mix and match will drive you bonkers, as you already experienced.
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Tim
 
I've seen that before too. My ET-732 would be different from the lid therm by 20 or 30 degrees. But later on in the cook they would be almost identical. I say pick one and go with it. I use my ET-732 with the temp probe right at the grate - since thats where the meat is.
 
No idea why there were such disparities between those temp measurements.

While I've been generally in the "vent temp" camp...the sun, wind, or precip. hitting the dome will definately affect the temp there. I just don't think it's as much a factor as a grate full of cool meat. Why does that matter? Well, it certainly does if I'm cooking something on a bottom grate that hangs over the pan, like a couple of pork butts. I wish I knew what the difference in temp could be between that taken between a couple of eight pound butts on the top grate, and the heat hitting the fat caps of butts where they hang past the pan on the bottom grate. I guess an oven therm placed just inside the door would help with that.

Anyways, back to measuring at the vent, I cooked a couple of butts yesterday and was tempted to hang my probe between the two butts right below the grate since I wasn't using a bottom grate. Most of my butt cooks are overnight, so I haven't had to deal with the sun hitting the cooker like it was. My umbrella shade helped some, but I was really surprised at how hot my cooker was wanting to run.
 
I was wondering the same thing then someone mentioned something about the heatsink getting to temp (the water,sand,plate or meat) and pointed out that even though heat rises your grate is still closer to the heat source and will be hotter than the dome temp.I had no clue so I just go by my Maverick reading.
By the way,how did your gasket experiment work.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Don Reed:
...someone mentioned something about the heatsink getting to temp (the water,sand,plate or meat) and pointed out that even though heat rises your grate is still closer to the heat source and will be hotter than the dome temp... </div></BLOCKQUOTE>

I probably have mentioned the same thing, but it depends on where on the grate we're talking about, and where the meat is.

Even without all the meat on the grate to obstruct the heat circulation, the heat circulation is coming up next to the walls of the cooker.

In other words, the queastion is just what is the difference between the temp hitting the outside edge of meats on the bottom rack compared to the temp hitting the bottom of the meats at the center of the racks. This difference is greatest at the beginning of a cook, and surprisingly, it doesn't seem to be enough to warrant turning butts around if two to a grate, at least cooking at typical bbq temps under 275*. Some do, but at least I haven't found it necessary. I just try to turn the thickest side towards the outside.
 
The gasket is working out well. I think it has formed the seal that I needed for better temp control. Also, now the coals go out when I shut down the vents.
It's just very strange to me that I can have 3 probes and each one reads differently. Not only that, but the amount they vary, varies from just a few degrees to 30 or more degrees....weird.
 
Well just temp @ one spot. And always use the same spot. Then you will know what time and temp the meat will be perfected at.

Have you temped the grate in your oven? Bet the oven termo is a few F off. But that dont make you put 3 probes in it?

A long time ago a very wise old man (Ben Franklin) said, "a man that has one clock knows what time it is and a man that has two is never really sure"
 
As mentioned, using multiple thermometers can drive you nuts. Best to get to know just one therm and use that as a guide.
 
The WSM therm is so steady, I just wanted to see how accurate it really was. When the therm in the vent started going crazy by 30 to 40 degrees, I had to find out what the grate temps really were. Is this indicative of the WSM therm?
 
D Arita - I'm still not sold on the lid therm thats why I rely on my Maverick so much. I've made several posts about the bad (so it seems to me)luck I've had with the lid therms so with the one I have now reading a pretty much constant 15 degrees lower than my Maverick I've learned to live with it. However I do try to keep my grate level therm in about the same area every time. I know this doesn't answer any questions but hopefully you'll find the happy medium the way I did.Like I've stated before,they work great to a certain point then stop rising altogether so the boiling water test shows they're good. I must also mention that a digital therm is going to be more sensitive to temp changes than ,I guess you'd call them analog/mechanical,therms.
 
I had some weird temp readings when I was doing two pork shoulders last weekend.

The 22.5 temp gauge and 732 were pretty close for a while, but when I took the top off about 1hr into the cook, and then placed it back on the WSM temp gauge shot to 350 plus, while the 732 readout stayed at 275.

It wasn't until 8 plus hrs into the cook that the WSM gauge went back down to a more normal operating temp. I just went by the 732's readings, and the shoulders came out great.

Not sure what caused the WSM's gauge to shoot so high after they were pretty close to the 732's for about an hr.
 
I would imagine with the internal capacity of a 22.5 WSM there would be some variance between the grate probe and the weber temp guage which is located near the top, but 20~30 would seem a bit much.
 
Sorry to say that your experience is pretty normal. I have and do cook on several WSM's and this is the case. All have been within 10 deg of accurate in boiling water. You are measuring in the air stream and in the dome, 2 different places= 2 different readings. I do not reccomend grate temping because of the meat will cause off readings, use the vent stream or just note that the dome is off by x deg and roll with that!
 
I'd have to agree with Glenn and the others in regards to the difference in the lid and the air stream at the vent. Also the differences in measuring with the 732 and the analog lid thermo.

I just recently got a 732 and I can't believe I waited so long. It's frigen awesome!
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Think of a smoker like an engine. They're both air pumps, taking in air and moving it out by burning fuel. The vent temp should be the most accurate for the temp. flow through the smoker. Like measuring EGT's from an engine in the exhaust stream vs. measuring temps from the block.

I haven't used the 732 enough to get a feel for the difference or accuracy of the grate temp vs vent vs anywhere else though.

As for the built in lid thermo. has anyone replaced it with one that's supposed to be more accurate, like the giant Taylor Weekend Warrior? I have one still in the package because I'm not sure where I'll want to use it, if at all. Reviews show it being extremely accurate compared to a good digital.

Might be interesting to clip the 732 thermocouple on the built in thermocouple and see what they do.
 
Someone else posted this idea on another thread and I've been watching my temps to see if it's valid.

The meat is cold when we put it on and the Maverick is near the cold meat so the Maverick reads lower. As the meat heats up then the Maverick is less affected by the meat. I record both temps and go with my best guess. I tend to rely on the Maverick more than the lid.
 
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