Temp Problems on UDS

Discussion in 'UDS Builds' started by freshmeat, Mar 30, 2010.

  1. freshmeat

    freshmeat Smoke Blower

    I completed my UDS build and did a seasoning smoke to learn nuances of unit. I placed three probes on the top grate and let it rip. I had up to a 60* variance in the temps registering by probes depending on how many caps (lower) I had off. I had a 40+* difference when I got it around 275*.

    The next day I checked my probes and found I had one bad one, and pitched it. Started another fire, and was getting a 40* - 50* difference again on the same rack. Probes were pushed through onions roughly 2-3 inches apart. The difference was consistent as I would open and or close caps and let settle for at least 30 minutes before making any other adjustment. (For example, when I would take a cap off and let stabilize both would readings would raise but still be ~50* apart.)

    I did notice early in the burn I had some smoke seeping out from where lid sits on barrel, later in the burn this was not present. I would not have believed this without seeing it, my lid fits tight enough that I can lift the entire barrel up using handle on lid when pressed on.

    I had probe wires running through weber lid vent holes (always wide open). This is a pain in the ass. Do I need to worry about drilling holes at grate level to allow for probe wire to pass? I have always left my probes in after pulling finished product and while they are wrapped in foil. I have done this because it seems when I have pulled probes to wrap a geyser of juiciness comes pouring out of probe hole. Am I misguided on this as well?

    I did construct a square charcoal basket and have included a picture at the beginning of the burn. I have it raised up 3" from ash pan, my ash pan is a cookie sheet I trimmed to size (it does have about a 1 inch side...should I flatten this?).

    I can't believe I can screw this up, but somehow I have. Needless to say I am more than a little bummed out. I would appreciate any and all help.
  2. rbranstner

    rbranstner Smoking Guru OTBS Member

    Well I do have somewhat of a similar problem as you do to a point. Pretty much all the time when I am smoking I get different readings from my probes depending on where they are in the smoker. I always have two digital probes and one analog probe. When I first start the smoker its not uncommon to have all three probes read something different. Yes it is kind of frustrating and I know my probes are dead on. I just wait it out and usually when I get the meat on there and am smoking for a while everything starts to even out. I know it can depend on where you probe is ie. if one probe is towards the center and the other is at the outside they can read different because the coldness of the barrel or what not. I don't really have an answer why they can be so different and then all of a sudden they will all read the same. I just don't sweat it as long as I am in the 200-250 range I am happy and nothing that I have cooked on there has come out bad. Hopefully some of the other guys can shead some light on this story as well.
    Oh about your probes yes I do drill two small holes for my probes to go into. Or if you want to leave them in your meat when you remove them then I would suggest cutting a very small V or a slit at the top of your smoker so the cable can go from your reader into your smoker probe without getting smashed in the lid.
  3. ddave

    ddave Master of the Pit OTBS Member SMF Premier Member

    What he said on the temp differences. [​IMG]

    With the drum you are using a very small hot fire to heat a much larger space. It works really well and gives very long burn times. It can be frustrating if you're one of thoes folks who likes to see the same temp over every square inch of the grate. [​IMG] I used to be but I got over it. As the fire works its way around the charcoal basket, the temp profile over the entire grate is bound to change. Plus when it's warming up, there is a huge difference between the center and the outside edge. Even after it is warmed up (I'm talking an hour and a half or more after lighting) mine still may have a 40° difference.

    I just put the meat in the center, get it in a range I like, and go with it. I've found smoking to be a whole lot more relaxing once I stopped stressing over the temps everywhere on the grate. I've never really had a single piece of meat undercooked on the edges. There is quite a bit of reflective heat in a drum so they tend to cook pretty even.

    About the probe wires . . . I drilled a hole in mine to pass the probes through. I never really noticed much juice escaping when I pulled the probe but if you're concerned about it, rbranstner's idea about the V notch sounds like a good way to go.

  4. smokin' dick

    smokin' dick Smoking Fanatic

    I don't think you have screwed up anything. Drums seem to run hotter in the center than near the edges. So some say. I have never checked the temp variation across the grate so I'm no authority on that. I do prefer to use a diffuser plate on top of my charcoal basket. It accomplishes two things. Well, maybe three.

    1. Seems to even out the temps side to side.
    2. Keeps some of the juices and fats from hitting directly on the coals for a
    less greasy smoke and flavor.
    3. Keeps flare ups to a minimum.

    Just some thoughts for you.
  5. meateater

    meateater Smoking Guru SMF Premier Member

    Calibrate your therms before you use them. I have a analog therm on my lid that runs 250* consistent, I just added another one about a foot down from the top just for the heck of it. I use my Weber Style Wireless Therm poked in the meat and double check when close to done with a good old chefs analog meat therm. So far so good. I also keep my therm unit away from the smoker itself and wrap with foil on the inside.
  6. badfrog

    badfrog Smoking Fanatic SMF Premier Member

    Hey there FreshMeat,
    Sounds like the variance is just the way the UDS works...it makes sense when you consider the heat coming off the basket is more in the center and is going straight up, so the sides would be cooler. I just started mine today; got the top off, vent holes cut and the pre-burn to clear it of all the nasties... as soon as I can I will be running the same tests you did - I will let you know how it goes.
    What did you finally decide on the outside? did you leave it, paint it?
  7. 200xga

    200xga Newbie

    im new to smokin but relaxing is the key. take two readings one in the center and one on the side and base everything on those readings. keep it simple. that is what i did and it works great
  8. ddave

    ddave Master of the Pit OTBS Member SMF Premier Member


    Yep. Find out what the difference is center to edge, take it into account when you load it up, relax and let it cook. A lot of times I won't even put the digital in when I put the meat on. I know my Teltrhu dial thermo should be between 180° and 200° for 240ish in the center. With the long stem thermo, I just set the pointer at 245° and peek at it once in awhile. If I'm smoking something overnight, then I'll put the ET-73 in so it will beep at me if something gets wacky. Usually doesn't though as the drum runs pretty steady.

  9. freshmeat

    freshmeat Smoke Blower

    Thanks to all for the input. I will admit I can get somewhat anal at times, and the initial wide variances on temp differences was giving me a little gas.

    I drilled a hole for probes to be introduced, much easier.

    I bought a couple 12" turkey fry therms (Outdoor Gourmet from Academy $3.99) to place directly under each grate. One of the new ones was off, going back.

    After a period of time temps did get much closer from different probes...I am R E L A X E D and good with it.

    No way can I get duration of burns described here...want to achieve a long butt session with minimal hassle, and my never attempted brisket smoke, which from reading can be a marathon. I am using Kingsford (blue bag) briquettes. Either the square design (volume not issue after enlarging) or this as a fuel source is the issue. I want to go with a round with a basket.
  10. meateater

    meateater Smoking Guru SMF Premier Member

    My UDS runs about 25* hotter around the edge, I also have a large water pan in mine. For me it works great. Best way I can describe it is I'm running a lang style standing up, indirect smoke in a different design.
  11. freshmeat

    freshmeat Smoke Blower

    I will add another level / grate to try out a water pan and grill functionality you described. I want to get settled on a permanent basket first.
  12. ddave

    ddave Master of the Pit OTBS Member SMF Premier Member

    You might try the Kingsford Comp Briquettes. They burn hotter than the blue bag and make very little ash in comparison. I have done several butt smokes and brisket smokes (14 pound packers) on a single load with fuel left over.

    Be aware that if you add a difuser plate or water pan you will use a lot more fuel than without. I'm not saying they are a bad idea, I have used a difuser plate a time or two. I'm just trying to make you aware of their impact on fuel use.

  13. meateater

    meateater Smoking Guru SMF Premier Member

    Take your time and experiment, that's have the fun of smoking food. I'm still experimenting after all these years.

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