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Temp craziness

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Boileregger
Boileregger Posts: 614
edited September 2012 in EggHead Forum
Just got the PartyQ and was using it for the first time on spatchcock chicken. I usually do raised direct at 400 dome so I clipped the PartyQ to the grid and set it for 375. When the PartyQ was holding at 375, the dome thermo read 325 and my Maverick, which was clipped a few inches away from the PartyQ was showing over 400.

So, figured it was time for a boiling water recalibration, which I did this morning on the dome thermo and PartyQ (Mav manual says not to submerge probes). Both were perfectly calibrated.

While I know this isn't a big deal, the engineer part of me wants to understand how I coul be getting such different readings. Any thoughts?
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  • Skiddymarker
    Skiddymarker Posts: 8,522
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    I agree, inquiring minds want to know. The reason for a difference between dome and grid is known, the question is difference between grid (375 for PQ) and grid (400 for Mav). Because you were direct, IMHO, the lump may have different heat characteristics for the two probes, that is one is over hotter coal than the other, even though they are only one or two inches apart. The difference is only 25 degrees, how long did you observe this difference? Did it flucuate and did it remain constant?
    It would be interesting to see if the difference exists when both probes are clipped to the center of an indirect grid sitting on a setter where the effect of lump temp difference is minimized. Perhaps we could ask you to perform an experiment.....
    Delta B.C. - Whiskey and steak, because no good story ever started with someone having a salad!
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  • Boileregger
    Boileregger Posts: 614
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    No the difference was not constant, what I reported was average. At one point the Mav was as much as 50 degrees difference. Also what puzzled me about the dome was that I thought the dome would be higher than the grid, not lower.

    I'm doing some BBs later today, I'll be interested to see if everything is closer going indirect and keeping the lid down so much longer.
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  • Skiddymarker
    Skiddymarker Posts: 8,522
    edited September 2012
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    For indirect cooks, pork shoulder on my MBGE, I usually note a difference of 25 degrees where the dome is less than my Mav on the grid. Yesterday's cook the Mav was holding at 275, the dome thermo held at 250. Makes sense as the grid is closer to the heat. (I think)

    For direct cooks, I seldom use my Mav, it is spec'ed for temps <572. 

    Regarding calibration, I think the Mav manual instructions are to not immerse the probes because some folks might just drop the probes, cable and all into boiling water. Can't see why you could not hold about 1/2 of the food probe or the pit probe into a pot of boiling water, trying to minimize the amount of steam that contacts the probe cable junction.  
    Delta B.C. - Whiskey and steak, because no good story ever started with someone having a salad!
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  • gdenby
    gdenby Posts: 6,239
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    Some of what you observed is because the cook was direct. Most of the energy coming out of burning lump is emitted in IR, not hot gases. Anything in direct line w. the glow is going to be a lot hotter than the air even up in the dome. Because the raised position in the Egg is suifficiently far away from the burning lump, the IR effect is lessened to the point where most foods can be cooked w.o. burning if watched. Put those same foods at the lower position for the same time, even tho' the dome reads the same, they will char.

    Its not as specific as having 2 probes on the grill, by I often do burgers raised, direct, and if the fire has not spread among the coals a lot, I often can have one burger near burnt just inches from another that is still barely browned.  I've tried stacks of disposable grill toppers to diffuse the heat, but even 5 or 6 of those don't even out the hot spot effects from uneven burning lump.
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  • Skiddymarker
    Skiddymarker Posts: 8,522
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    @Boileregger, I knew someone would have the reason, @gdenby, thanks for the information.
    Delta B.C. - Whiskey and steak, because no good story ever started with someone having a salad!
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  • GLW
    GLW Posts: 178
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    I have a question.  Would the dome and the grid temp "even" out over time on a long cook? 
    When in doubt add more pepper.
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  • nolaegghead
    nolaegghead Posts: 42,102
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    GLW said:
    I have a question.  Would the dome and the grid temp "even" out over time on a long cook? 
    I have seen them even out before on a long indirect cook, but it's rare.  Doubtful for direct - the grate is closer to the coals and gets more infrared radiation.
    ______________________________________________
    I love lamp..
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  • GLW
    GLW Posts: 178
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    Thank you.  I've noticed that on my 220 degree 18 hour indirects the dome and grid do even out and that made sense to me.

    When in doubt add more pepper.
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  • Boileregger
    Boileregger Posts: 614
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    Didn't get to test with the BB's yesterday. Sick kid and unhappy wife, so was doing good just to get the ribs done. Thanks for the info everyone.
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  • xraypat23
    xraypat23 Posts: 421
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    for a raised direct cook, i clip the lead for my ique to the dome temp gauge. As stated about you want something blocking the direct infrared heat from the probe. At 400 you're right on the edge of what that probes designed for. Some dripping grease can have a 500-600 flare up real quick
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