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MES 40 - Troubleshoot cause of temp reading on display higher than actual temps

Discussion in 'Electric Smokers' started by hkeiner, Jan 20, 2011.

  1. I purchased a MES 40 (model 20070710) in October 2010 and am very happy with it. However, I have found that the temperature reading on the MES display consistently shows 20-30 degrees higher than the temperature shown on my Taylor 1470N digital thermometer. (I checked the accuracy of the Taylor using the boiling water method and found that it was within a few degrees of 212). To compensate for the MES display error, I set the temperature on the MES control unit 20-30 degrees higher than my desired temperature. This works OK for things I want to smoke at 225-250 (ribs, butts, etc) but it does limit me from smoking at higher actual temperatures (e.g., 275 degrees for chicken, etc.). I moved the Taylor probe around a bit inside the MES box and still found the disparity.

    I am thinking that either one of the sensors inside the MES is at fault or the control unit on the top of the MES is at fault.   There are two sensers on the back panel of my MES 40. One is at the top left (sensor #1) and the other is in the middle right (sensor #2). I have read that the #1 sensor is called a "limit sensor" and the #2 is called a "temperature sensor". While I get the general idea as to what these sensor may do, I don't know how to test them or if they can be a likely culprit.

    In short, these are  my questions:

    - If one of these sensors can cause a display error, which one is it most likely to be?

    - Can the sensors be bench tested using a multimeter, and if so, are there any specs (e.g., ohms/voltage at a specific termperature) for testing them?

    - Is it more likely that the control unit is at fault, and if so can it be tested using a multimeter or any other way?

    For cars, appliances and such I don't generally like to throw parts at a problem without first diagnosing a failed part. Perhaps it is not feasable to do this on the MES and that guessing is more practical. If so, I would appreciate your "guesses" before I order any sensors from Masterbuilt and remove the back panel to replace them (which would be a pain).

    Thanks in advance for any responses.

    Last edited: Jan 19, 2011
  2. Would also like to know....  Mine is off too
  3. SmokinAl

    SmokinAl SMF Hall of Fame Pitmaster Staff Member Moderator OTBS Member ★ Lifetime Premier ★

    Mine is off as well, but the other way. I set it at 215 if I want to cook at 225-230.
  4. markk

    markk Smoke Blower

    I have the same Model # smoker as you. I have also noticed that the temperature displayed on the controller is lower than my Maverick thermometer when smoking a load of meat. I compared the two temperatures one day with the smoker empty and they seemed to match. Not sure what that means though
  5. porked

    porked Smoking Fanatic

    Try placing your Maverick probe in different spots inside the MES, my guess is you'll get different readings, I know I did.
  6. Bearcarver

    Bearcarver SMF Hall of Fame Pitmaster Group Lead OTBS Member

    My Maverick is nearly always higher than the MES digital, but they get closer after the smoker comes to the set temp, and simmers down awhile. The Maverick is quicker to go up & quicker to come down. It's just the nature of the beast.

    I don't really worry about what the MES reads. I only use it to get me into the ball park. I put the Maverick next to the meat, and go by that. Then I make adjustments going by the Maverick.

    It doesn't matter what the temp is where that #2 Temp Sensor is. It matters what the temp is where you have your meat.

    Sometime try sticking the tip of your remote probe about an inch from that #2 temp sensor, and see what they read then, for a few cycles.

    BTW: I see your problem, if you can't set it higher than 275˚, and your MES is 20˚ lower than actual, you really are only able to set it at 255˚, but try that "Sticking that tip of your tested remote probe within an inch (not touching) of that sensor" and see what happens through a few cycles.

    Last edited: Jan 21, 2011
  7. tjohnson

    tjohnson Smoking Guru Staff Member Moderator Insider OTBS Member SMF Premier Member

    My 1 year old 40" MES is off 15° on the hot side, compared to a brand new maverick ET-732 and my "Brand New" 40" 40" MES is off 20° and warmer temps, but at freezing temps, it's off 32°.  i use it only for reference and use a Maverick ET-732 for real temps.

    ncsmokeu likes this.
  8. doctord1955

    doctord1955 Smoking Fanatic

    what is your high and what is your low temp as smoke cycles?
  9. Bearcarver

    Bearcarver SMF Hall of Fame Pitmaster Group Lead OTBS Member

    Normally, mine starts at 2˚ below the temp setting, and shuts off on the temp setting, but if it's real cold & windy out, it may drop a few more degrees lower, after the element kicks on, and then coast up a few degrees above the setting, after the element shuts off.

    I hope that makes sense.

    If it doesn't, let me know & I'll try again.

    Maybe this is easier to understand:

    Set heat at 200˚

    On at 198˚

    Off at 200˚

    Cold & Windy out---Set at 200˚

    On at 198˚

    Off at 200˚, but coast up to 203˚, after element shuts off.

    On again at 198˚, but keep dropping to maybe 194˚ before temp starts rising again.

  10. I placed the Taylor probe close to the #2 probe and saw that the MES controler still showed 20-30 degree higher than the (calibrated) Taylor probe.  This disparity is pretty constant during the entire smoke period. I can not heat the MES up to 275 (when desired) because the controller wont heat the MES up past 245-255 or so (thinking that it is at 275). If the difference went the other way (i.e., the Taylor temp was higher than the MES temp) then I would not bother with this problem since I could easily heat the MES up to 275 when desired.

    Back to my original question, can anyone guess if replacing the #2 probe or replacing the controller is more likely to fix this problem? I welcome any guesses based upon prior experience in troubleshooting this type of problem or any technical knowlege on how this whole probe/controller thing works.
    Last edited: Jan 23, 2011
  11. Bearcarver

    Bearcarver SMF Hall of Fame Pitmaster Group Lead OTBS Member

    Mine is the other way around:

    When my MES says 250˚, my other probes say from 270˚ to 290˚, depending on where they are. If I take the MES up to 275˚, the others are at 300˚ or higher.

    The remote probes are the accurate ones---This includes the MES meat probe, so other than using the digital to make the settings, I ignore what it says, and go by what the remote probes say. 

       Since yours is the opposite, you can only heat your smoker up to 245˚/250˚ (Actual temp), when your MES is set & reading 275˚. I would contact MBTechguy (Darryl), and explain it to him. Since you checked your remote probe in boiling water, I would think it is your controller, but contact him and see what he says. He will probably send you another controller, but I'm just guessing, because I know how good a rep he is.

    franko likes this.
  12. garyc

    garyc Smoke Blower

    My MES 30 /SS is way off as well. What I thought was 220 deg turns out to be 240. It's OK now that I know about it. I wish there was a way to adjust it though.
  13. fife

    fife Master of the Pit

    Yep mine is off also I put some thick foil folded over and place it over the smoke box it seems to even it out very well. I tryed the tile but it did not do well at all.
  14. Can you please show a picture of how you placed the foil over smoke box and what are the measurements of the foil?  Thanks for the tip.  can you sent that to my message bax also?

  15. uhmgood

    uhmgood Smoke Blower

    i have the MES30 , same problem but i did notice that the longer the cook went on the closer and closer my maverick and the probe in the unit came together in temp. i have almost stopped using the mav and just relie on the one in the unit , when it gets close to what i want i check with an instant read , seems to be working out so far
  16. i set my mes 40 @275, i get maverick readings (and it reads boiling water at 212) and it will say from 220 to 245 around the MES
  17. Bearcarver

    Bearcarver SMF Hall of Fame Pitmaster Group Lead OTBS Member


    I have noticed this at times too!

    I think it's because during the beginning of the smoke, the meat is cold, and the maverick probes are more sensitive than the MES sensor, so the maverick runs up and down more, and the MES readout tends to stay more steady. Then later in the smoke, the meat is no longer cold, so the Maverick settles down & tends to get closer to the MES temp reading. Hoping you can understand my translation from my brain to my typing finger.

  18. uhmgood

    uhmgood Smoke Blower

    bear , i think your absolutely right , makes sense to me
  19. daricksta

    daricksta Master of the Pit OTBS Member

    I know this is an old thread, but just wanted to add my comments. I have a MES30 and I also use a Food Network thermos made by Taylor and equivalent to their 1471. I calibrated it and found it to be within 2 degrees or so of accuracy at 212 and 32. I stuck the probe through a potato as advised by Todd Johnson and stuck it inside my MES to calibrate its temp. During warm up, the MES digital temp displayed 20 degrees higher than the FN/Taylor. But when it reached my target temp the discrepancy fell to only 2 degrees higher than the Taylor and remained there. During that same session I cooked two racks of ribs, inserting the probe from the Taylor into the ribs on the top rack. The ribs turned out beautifully.

    So now, when I use the smoker, I set the digital thermos 2 degrees higher than the actual target temp I want. Since I know the Taylor may be two degrees low, this should ensure I get the temp correct on the smoker. Hope that isn't too confusing.
  20. sigmo

    sigmo Smoking Fanatic ★ Lifetime Premier ★

    I agree with that!
    I would not replace a probe when we don't know if there is a problem, and if so, if it's the sensor or the controller that's out of whack.
    Make sure to correct for your elevation above sea level.  Where I live, water boils at about 199 degrees F.

    Also, it's quite difficult to compare readings on different thermometers or probes.  So unless you have an excellent way of thermally coupling the two probes under test, and you're accounting for thermal time-lags in the probes, etc., don't get too worried if you get different readings between different thermometers/probes.

    I just posted a very long-winded diatribe on this subject here:


    Hopefully it'll be helpful.

    That doesn't mean your controller/sensor ISN'T out of whack, but I'm just saying that I've seen this sort of complaint so frequently in our laboratories, that I know how easy it is to think you've got a defective thermometer/sensor/controller when actually, you're just seeing the typical variations from one place to another in an oven (even inches apart).

    Unless you go to great lengths to make sure the various thermometer probes are thermally coupled to each other, it's difficult to do a valid comparison.

    In my MB 40, the sensor that the controller uses to operate the heater appears to be a slender probe poking in an inch or inch and a half through the back wall about 2/3 of the way up.  Keep in mind that any sensor or thermometer can only report the temperature that it is "seeing" right at that one point.  And that may not be representative of the temperatures elsewhere in an oven, cooler, or whatever.  One would hope that the designers experimented with the position for the controller sensor and chose a place that gives good results.  But who knows?

    Anyhow, before doing anything rash, make sure you're performing a valid test on the probe in question.