MES40 Temp Inaccuracy Making Me Crazy

Discussion in 'Electric Smokers' started by montol, May 13, 2017.

  1. Hello,

    I'm going a bit batty trying to get a consistent temperature going in my MES40. I have the new gen 2.5.

    When I first got it, it was running hot. For example, my Maverick 733 would be reading 250F when my MES40 was set to 225F. This remained true for the first 3 smokes or so, and the temperature difference between the two remained around 15F-25F depending on how stable the temps had become.

    Today, I've got a full load of ribs and chicken, and I've somehow magically got the exact opposite issue. My MES40 is set to 275F, and reading at about that temp, and my Maverick is struggling to get back up to 225F.

    I've reset the Maverick, replaced the batteries, and swapped the probes just to see if I was having trouble with one or the other. No change.

    Is this normal? Has anyone else had this issue?

  2. bbqwillie

    bbqwillie Smoking Fanatic

    The MES temp probes are notoriously inaccurate. Believe your Maverick. You did test the Maverick probes with the boiling water test, didn't you?
  3. Yup, did the boiling water test early on. One probe is 4F different than the other, but I figure that's reasonable.

    So...basically if this issue continues where the MES40 isn't putting out enough heat anymore, then I'm going to have to do something through warranty service? I can't do chicken properly if I'm struggling to hit 225F...
  4. bbqwillie

    bbqwillie Smoking Fanatic

    How many pounds of food did you put in the smoker? Did you preheat to temp and then load cold meat into the cooker? Is the Maverick ambient probe close to any cold meat?
    Last edited: May 13, 2017
  5. bearcarver

    bearcarver Smoking Guru OTBS Member

    Could be where you have your Maverick probe.

    Also what a lot of people do is put too much stuff, like Pans or a lot of meat, not letting enough space between the items to allow the heat to pass through to all parts of the Smoker.

    In other words, "f you have a full rack on Number 3 position, and your Maverick on Number 2 position, the temp could be at 250° below the full rack, and only 225°, or even 200° above the full rack, because the heat can't get through the full rack."

    Also if you have the Window in the door, like my MES 40, make sure it's not facing toward the South.

    The Sun can shine through the glass onto the heat sensor on the back wall of the smoker & the heating element will shut off early, thinking it's hotter in there than it really is.

    Just a couple of Possibilities.

  6. chef jimmyj

    chef jimmyj Smoking Guru Staff Member Moderator Group Lead OTBS Member

    The variation the first run is typical. The opposite effect was more likely from the big load of cold meat. I have seen this with mine. Over time the different readings get closer and closer together...JJ
  7. tiros

    tiros Newbie

    I have similar issues. I read a good 30 degrees higher than actual. Everyone says just up the temp till it reads right, that's not a fix!. If you read 30 degrees higher than actual, your max temp will be limited to 245, no matter what you set at.

    I have an engineering background, so I have investigated.

    The controller in my MES40 uses a resistive thermocouple to monitor the oven temp. The TC feeds a 5k resistor on the PCB, and this voltage divider feeds the analog to digital converter pin of the MCU. I was unable to dump the firmware code of the controller chip to modify it there, so I decided to replace 5k R with a 5k pot, and was able to adjust to get my oven up to full temp, with proper display. When the oven cools down, the error then appears  for the lower temperatures. Conclusion: Overall poor design. The probe itself sucks, its only good for about 100C. Resistive thermocouple is not linear. The controller usually "flattens out" this non linearity by software.The problem is, at higher temps, the resistance does not change too much compared to mid range temps. It is therefore harder for mcu to resolve the higher temps to any accuracy, the problem is worse from probe to probe, at higher temps, but not so noticeable at mid range. Changing the bias with a pot, moves the curve, but its not right.

    I am working on a internet enabled full replacement controller, with PID, multiple probes, and graphing. I discovered this problem while interfacing to the stock probe. I haven't decided to use the stock, or to remove it and replace with RTD type sensor. Not real clear how to remove the stock probe. I don't want to drill out all those rivets.
    Last edited: Jun 5, 2017
  8. bearcarver

    bearcarver Smoking Guru OTBS Member

    I have no idea what your technical words mean, nor am I interested.

    All I can say is many of the MES controls are close enough, and if the temps are actually higher than the MES digital read-out, like mine, enjoy it.

    However if the actual Temp is more than 20° less than the MES digital read-out, that would mean you can't get higher than 255°. If I couldn't get above 255° actual temp, I'd be calling Masterbuilt to get it fixed or a new Smoker. We paid for a Smoker that goes to 275°, and I think they claim +/- 15°.

    Masterbuilt Customer Service has been proven to be quite good.

  9. tiros

    tiros Newbie

    Well if your happy, then good for you!

    I'm not, and from a casual glance of this forum, it appears I am not alone. I am working on a real solution, and it is technical, so if you can't contribute then simply don't.
  10. dr k

    dr k Master of the Pit

    Right. With the fixed Mes sensor on the back wall , close is all you can expect from it being in a vertical smoker, considering your model with 4 or 6 racks. The second to the bottom rack on the 4 rack gen 1 40 is where the sensor is and is hotter on the bottom rack and gets cooler as you get to the top. So when people do the PID with the thermal couple being able to sit on any rack your getting as close to perfect as possible. Moving the water pan to a different level chamges temps at different levels with the same mes setting. Until MB tethers their chamber probe so it sits on any rack like their meat probe your stuck with moving the water pan or food. I'm sure most everyone can get to 275*F it just depends which rack/racks. My mes averages 260-265*F on second from the top rack with a calibrated therm with the controller maxed a 275*F. If I want 275*F in my smoker I drop down into that zone. My smoker has a few degrees coasting above and below the set temp vs. many at 225*F. I am finding I like my smoker and results with maxing the smoker and using foil drip pans with the meat elevated on a small cooling rack and keeping my oval water pan up on thre second level from the bottom and can use the top three racks. This my favorite set up.
    I prefer 9"×13" alum disposable pans but had this small disposable cookie sheet I needed to get rid of so I left the rack out and put the cookie sheet directly on the water pan.

    I'm happy and can get the temp I want redecorating the inside so to speak. So no controller mod until something fails
  11. bearcarver

    bearcarver Smoking Guru OTBS Member

    Excuse me!

    I didn't say that to be a Smart-arse. Everything I say on this forum is usually meant to help more than one person.

    Plus you missed the important part of my comment in your Quote:

    However if the actual Temp is more than 20° less than the MES digital read-out, that would mean you can't get higher than 255°. If I couldn't get above 255° actual temp, I'd be calling Masterbuilt to get it fixed or a new Smoker. We paid for a Smoker that goes to 275°, and I think they claim +/- 15°.
    Masterbuilt Customer Service has been proven to be quite good.


    That said, If you can improve on something That's Great.

    Last edited: Jun 5, 2017
  12. bearcarver

    bearcarver Smoking Guru OTBS Member


    Everybody's MES is different, and no matter how perfect one thinks his control is working, the temp is going to be different from one position to another.

    The real solution is as always---Learn your smoker & how to make minor adjustments to make things work for you.

  13. tallbm

    tallbm Master of the Pit

    I've made a ton of modifications to my MES that I am still testing, all in the hopes of resolving or reducing the types of issues you see.

    What it appears I am finding is that you will simply have different heat levels at different rack positions as you add meat.  As mentioned before I believe this is due to the heat simply being blocked and trapped by meat on racks as the heat travels upwards.

    I have installed a convection fan and I am now using a PID controller which have both helped in eliminating the large temp swings I was getting in my MES and improved the difference in temp between bottom rack and top rack when loaded with at least two racks of meet.

    I am thinking the difference in temp racks is just always going to be there no matter what.  I am thinking it is impossible to get an even temp at all levels of the smoker once meat is added due to the size (volume) of the smoker, the heating element arrangement (small and in one location), the way air flows inside, and the fact that air is moving OUT of the smoker through a vent the entire time.

    I will still continue to play around with my smoker to try and resolve as much of this as I can but I have to face the facts.  These smokers are not ovens no matter how similar the smoker feels to an oven.  I will continue to play around and see how I can improve things because I want to get the most stable environment I can make and I enjoy the challenge of tinkering with all of it.   

    Right now I see best results when using the bottom two racks.  That is where your probe is located in any case.  I see that only loading 1 rack of meat yields the most consistent temps and going beyond 2 racks of meat is often asking for chaos if you expect to keep them close in temp to one another.

    If you are doing chicken and want to try and get the best cook on it then the bottom rack is your friend, though I have always had trouble in the stock MES40 getting chicken skin to be edible.  Bottom rack, max smoker temp, and skin down towards the heating element has been the best results for me for chicken skin on cut up chicken.  A vertical chicken smoking rack (like the beer can style) on the bottom rack, max smoker temp, have been the best results for me with a whole chicken.

    I hope all this info helps and I hope you can tinker enough to be satisfied with your results :)
    Last edited: Jun 5, 2017
  14. tiros

    tiros Newbie

    I am quite certain the oven has PID control in its firmware. PID is only an algorithm. It only works as good as the values plugged in. Since PID controls ramping and holding, I wouldn't be surprised if they purposely messed with the algorithm to enhance the "on" time of the burner in hopes of producing more smoke. Such a strategy would lead to wider temp swings. If you use a smoke attachment, you don't really want that.
  15. I posted a tread awile back where you can build a PID controller setup for 30 bucks, mine works great
  16. jcam222

    jcam222 Fire Starter

    I am one who is completely dissatisfied with the temp control and inaccuracy of what it reports. I have within the first 100 days had to replace the temp probe, the digital display and power board for starters. This was their solution to two issues 1) The temp probe going completely bonkers reading over 500F even when hanging outside the smoker and more importantly 2) mid smoke on about 40 lbs of pork the temp dropping to what was reported as 187 about 4 hours in and the actual temp with my thermo showing at 300!!

    I have done a couple of smokes since then with no issues and then there is today. Preheated to 225 to do ribs, put in 4 racks and some trimmings and TWO HOURS later the digital display is reporting 212 which is what its been stuck at for an hour. Threw in a probe from my digital and its 243. The element is heating the whole time by the way. Its also 90f outside. 

    This things quality is garbage as far as I am concerned and when I call to complain their solution will again be to send me a box load of damn parts. lol as you can see I am pretty unhappy at the moment. 
  17. bearcarver

    bearcarver Smoking Guru OTBS Member

    Which racks did you have the 40 pounds of Pork on?

    Which racks did you have the 4 racks of Ribs on?

    Where did you put your Wireless probe when you got a 243° reading?

    Have you tried your MES while Empty to see if it's where you have the meat that causes some of the problems?

    Need more details to figure what causes these things.

  18. tallbm

    tallbm Master of the Pit

    Bear is right more info needed.  In any case if you want to rewire and go with a 3rd party PID controller it is actually much easier than it seems... it just costs a little money.

    On a good note the physical construction is pretty good other than some plastic parts cracking and such.  I've modded the crap out of my MES40 and I'm pretty happy with it.  I have about hit the max limitations of what it can do and I can basically smoke anything with few limitations in mine now.

    Here is the post I did on rewiring without having to pull off the back of the MES should you decide to go with a plug and play PID controller like the Auber ones.  Best of luck:
  19. hondo

    hondo Fire Starter

    Without getting into the how and why's of this discussion I have a question about temp variations in the MES30 that affects what I want to do..

    When making snack sticks (which is one big reason I got an electric smoker) and hanging them from rods these temp variations would make the different areas of the sticks done at different times. I want to make these and not have burnt at the bottom and raw at the top with a few inches of perfect in the middle. I don't know if PIDs, fans or anything else will really help so  how are people making these sticks with good results?

    Based on some comments above I could make some and put them on a single rack and try to get the goal temp for that rack but that would be a very small amount to sticks for each cook.

    So in the spirit of this discussion can anyone tell me how to make all areas get done at the same time?
  20. uncle eddie

    uncle eddie Smoking Fanatic SMF Premier Member

    I have had the same good experience with Masterbuilt Customer Service with my MES40.  I hope you find it just as good.

    Lately, my temperature sensor does not work well over my MES40 runs hot when I set it at any temp over 235F.  If I set it at 240F or above, it runs about 275F-285F because the temp sensor never climbs above 235F. I am actually liking this glitch.  
    Last edited: Sep 24, 2017

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